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RUCTION  OF  DISABLED 
MEN  IN  MOTION  PICTURE 
PROJECTION 

AN  ELEMENTARY  TEXT  BOOK 


By  JAMES  R.  CAMERON 

/nttrwtor  of  Projection 
The  Red  Crott  Institute  for  C-ipped  and  Diiabled  Men 


NEW  YORK 

THE   RED   CROSS  INSTITUTE  FOR 

CRIPPLED  AND  DISABLED  MEN 

1919 


GIFT   OF 


MOTION  PICTURE  PROJECTION 


INSTRUCTION  OF  DISABLED 

MEN  IN  MOTION  PICTURE 

PROJECTION 

AN  ELEMENTARY  TEXT  BOOK 


By  JAMES  R.  CAMERON 

Instructor  of  Projection 
The  Red  Cross  Institute  for  Crippled  and  Disabled  Men 


NEW  YORK 

THE  RED  CROSS  INSTITUTE  FOR 

CRIPPLED. AND  DISABLED  MEN 

1919 


C3 


ACKNOWLEDGMENT 

IS  HEREBY  MADE  TO  THE  NICHOLAS  POWER  COMPANY 

AND  MR.  J.  H.  HALLBERG 

FOR  THE  LOAN 

OF 

SEVERAL  CUTS  AND   PLATES 
USED   IN  THIS  BOOK 


V 


COPYRIGHT,   1918 

BY  THE  RED  CROSS  INSTITUTE  FOR  CRIPPLED 
AND  DISABLED  MEN 


MOTION      PICTURE      PROJECTION 


INTRODUCTION 

Fifteen  to  twenty  years  ago  the  motion  picture  was 
regarded  as  an  amusement  for  children  and  little  else. 
Today  the  industry  is  the  fifth  largest  in  the  United 
States.  The  motion  picture  now  commands  the  interest 
and  attention  of  leaders  in  every  field  of  endeavor  and 
it  is  judged  ky  the  high  standards  that  are  applied  to 
the  other  arts. 

The  development  of  the  motion  picture  in  mechanical 
and  artistic  perfection  has  brought  about  a  correspond- 
ing demand  for  highly  skilled  projectionists.  The 
poorly  projected  film,  notwithstanding  the  thought, 
expense,  and  effort  expended  in  its  making,  is  stamped 
as  a  failure.  The  man  who  stands  in  the  booth  "and 
merely  turns  the  crank"  is  as  obsolete  as  the  "Nickelo- 
deon." Into  his  place  has  stepped  an  artisan — a  man 
trained  in  applied  electricity,  optics,  the  theory  of  light, 
and  the  manifold  complications  that  are  entailed  in 
successful  projection.  No  man  is  permitted  to  operate 
the  machine  unless  he  has  a  city  license,  which  means 
that  he  must  pass  a  thorough  examination  before  he 
can  go  to  work. 

The  need  for  schools  to  train  motion  picture  projectors 
is  greater  at  the  present  time  than  ever.  Manufac- 
turers and  exhibitors  state  that  there  is  a  scarcity  of 
good  projectionists,  and  they  offer  ready  and  profitable 
employment  to  qualified  men. 


VI  MOTION      PICTURE      PROJECTION 

The  shortage  of  labor  caused  by  the  war  pointed  out 
the  necessity  as  well  as  the  wisdom  of  utilizing  every 
possible  unit  of  productivity.  The  experience  of  the 
European  belligerents  proved  that  it  is  possible  to  train 
cripples  for  trades  in  which  their  physical  handicaps 
do  not  debar  them  from  competing  successfully  with 
the  able-bodied.  Soon  after  America's  entry  into  the 
war,  a  group  of  far-seeing  men  realized  the  need  of  pro- 
viding training  for  the  cripples  of  industry  so  that  the 
experience  thus  gained  might  serve  as  a  basis  for  the 
re-education  of  the  returned  disabled  soldier. 

The  effort  of  these  men  culminated  in  the  establishing 
in  New  York  City  of  the  Red  Cross  Institute  for  Crip- 
pled and  Disabled  Men,  under  the  auspices  of  the 
American  Red  Cross.  Departments  of  industrial  sur- 
veys, research,  employment  and  public  education  were 
inaugurated  and  the  foundation  of  the  first  special  non- 
commercial training  school  for  the  physically  handi- 
capped in  the  United  States  was  built.  Classes  in  the 
manufacture  of  artificial  limbs,  mechanical  drafting, 
printing,  jewelry  making,  and  oxy-acetylene  welding 
were  begun,  and  in  May,  1918,  a  course  in  motion  pic- 
ture operating  was  introduced  with  James  R.  Cameron 
as  instructor. 

The  choice  of  motion  picture  projecting  as  a  trade 
for  the  cripple  was  based  on  the  knowledge  that  it  was 
one  of  the  growing  trades,  that  in  England  and  France 
the  cripple  had  made  good  as  a  projectionist,  that  the 
wages  were  good,  that  working  conditions  were  favor- 
able, and  that  almost  any  man  with  both  hands  intact 
could,  with  a  course  of  study  of  about  two  months  in 
duration,  acquire  sufficient  knowledge  to  enable  him  to 


MOTION      PICTURE      PROJECTION  Vll 

enter  an  operating  booth,  and  take  charge  of  the 
machines. 

About  twelve  pupils  responded  to  roll  call  during 
the  first  days  of  the  class  at  the  Red  Cross  Institute. 
Most  all  were  leg  cases,  either  paralysis  or  amputation. 
Most  of  the  men  had  to  support  themselves  while 
learning  but  they  applied  their  energies  to  their  task 
and  made  rapid  progress.  With  one  exception,  all  of 
the  men  who  have  taken  up  this  course  have  passed 
the  municipal  examination,  and  have  secured  positions 
through  the  Institute,  and  what  is  more  to  the  point, 
every  one  of  them  has  made  good  on  the  job.  The 
first  graduate  of  the  class  earned  sixty-two  dollars 
during  his  first  week  of  actual  employment,  and  the 
salaries  of  the  others  averaged  about  thirty-five  dollars 
per  week. 

The  course  of  study  in  the  motion  picture  operating 
class  in  the  Red  Cross  Institute  is  designed  to  be  as 
thorough  as  possible.  The  pupil  receives  training  in: 

(a)  Elementary  Electricity. 

(b)  The  Application  of  Electricity  to  an  Arc  Lamp. 

(c)  The  Construction,  Care  and  Use  of  Electrical  Ap- 
pliances,   such    as    Transformers,    Mercury    Arc 
Rectifiers,   Rheostats,    Motor   Generators,   Storage 
Batteries,  etc. 

(d)  Optics — Construction  of  Lenses. 
0)    Theory  of  Light. 

(/)    Construction  and  Care  of  Projecting  Machines. 
(g)  Handling,  Care  and  Repairing  of  Films. 

The  aim  of  the  course  is  not  only  to  fit  a  man  to  take 
the  city  examination  for  a  license,  but  to  give  him  a 


Vlll  MOTION      PICTURE      PROJECTION 

good  working  knowledge  of  actual  projection.  He 
must  make  a  certain  grade  in  his  work  both  in  theory 
and  practice  before  the  Institute  permits  him  to  apply 
for  his  license. 

The  equipment  at  the  disposal  of  the  students  in 
the  Institute  was  generously  loaned  by  the  Nicholas 
Power  Company,  the  Simplex  Machine  Company,  the 
United  Theatre  Equipment  Corporation  through  its 
President  Mr.  Hallberg,  Mr.  William  Fox,  Mr.  B.  F. 
Wyler,  and  others.  It  is  valued  at  nine  thousand  dollars 
and  consists  of  everything  necessary  to  a  mastery  of 
the  art  of  projection. 

The  equipment  includes  the  following: 

Power's  Motor  Driver  Projection  Machine. 

Simplex  Machine  installed  in  Asbestos  Booth. 

Acme  Portable  Machine  equipped  with  Mazda  Lamp. 

Cosmograph  Portable  Machine  with  Pencil  Arc. 

Hallberg  Motor  Generator. 

Hallberg  Economizer. 

Hallberg  Regulator  for  Mazda  Lamp. 

Step-Up  and  Step-Down  Transformers. 

Rheostats. 

Mercury  Arc  Rectifier. 

Stereopticons. 

Distributing    Board  fitted    with    the    various    House 

Wiring  Systems,  Ammeters  and  Voltmeters. 
Various  makes  of  Screens. 

Film  Measuring,  Cleaning  and  Re-winding  Machines. 
Vivatarg  Apparatus. 


MOTION      PICTURE      PROJECTION  IX 

VIVATARG  APPARATUS 

A  new  motion  picture  projection  machine  whose 
mechanism  is  automatic  and  controlled  by  sound  waves 
created  by  the  voice,  the  clapping  of  hands,  or  other 
noises,  reports  by  explosions,  etc.,  was  recently  in- 
stalled in  the  Red  Cross  Institute.  The  sound  waves 
are  recorded  by  a  telephone  receiver  connected  to  a 
system  of  control,  which,  instantly  a  sound  is  made 
by  the  voice,  etc.,  brings  the  motion  picture  to  a  stop; 
after  a  pre-determined  period  of  from  one  second  to 
one  hour,  if  desired,  the  picture  on  the  screen  resumes 
its  motion. 

The  Vivatarg  is  electrically  operated  and  automati- 
cally controlled.  It  is  especially  useful  in  connection 
with  lectures  and  practical  demonstrations  of  surgical 
and  dental  operations  and  of  the  construction  of  special 
apparatus,  for  the  picture  can  be  brought  to  a  sudden 
halt  to  enable  the  lecturer  to  explain  his  point  in  detail. 
To  accomplish  this,  the  inventor  had  three  obstacles 
to  overcome:  (1)  to  stop  the  picture  instantly  at  any 
given  point;  (2)  to  hold  the  picture  still  on  the  screen 
for  any  desired  period;  and,  (3)  to  prevent  the  burning 
of  the  film  while  held  stationary.  The  Vivatarg  per- 
forms all  three  functions  successfully.  It  is  a  mechan- 
ism that  offers  an  almost  unlimited  field  for  experi- 
mentation. The  Vivatarg  in  the  Institute  is  one  of 
three  machines  of  the  same  type  in  existence. 

A  FUTURE  OF  PROMISE 

From  the  beggar's  cup,  the  pack  of  pencils,  or  the 
"blind  alley"  job  of  watchman  or  messenger  to  the 


X  MOTION      PICTURE      PROJECTION 

position  of  motion  picture  projector — from  charity  to 
self-support — that  is  the  road  that  many  cripples  have 
been  encouraged  to  take.  If  the  public  will  help  the 
cripple  to  "come  back,"  if  they  will  regard  him  as  a 
person  with  the  same  ambition  and  the  same  right  to 
an  opportunity  to  succeed  as  the  normal  man;  if  the 
employer  will  give  the  cripple  a  chance  to  make  good 
on  the  basis  of  competency  alone — not  charity — the 
future  that  awaits  those  of  our  soldiers  who  return 
disabled  is  bright  with  possibilities. 

HARRY  BIRNBAUM 

Red  Cross  Institute  for  Crippled 
and  Disabled  Men 


p  • 
t-( 


Xll  MOTION      PICTURE      PROJECTION 


Powers  Cameragraph  No.  6B 


MOTION    picfUKE   'PROJECTION 


ELECTRICAL  TERMS 

It  is  necessary  for  the  projectionist  to  thoroughly 
understand  the  following  electrical  terms : 

Electric  Motive  Force.  Another  name  for  voltage  or 
pressure.  Generally  written  E.  M.  F.  The  volt  is  the 
unit  of  E.  M.  F. 

Ampere.  The  unit  of  current  strength.  The  quan- 
tity of  current  flowing  through  a  circuit. 

Ohm.  The  unit  of  resistance.  The  term  used  to 
measure  the  opposition  offered  to  the  flow  of  an  electric 
current.  The  amount  of  resistance  offered  by  a  column 
of  mercury  106  centimeters  in  length  by  one  square 
millimeter  in  cross  section,  at  a  temperature  of  zero 
centigrade. 

Direct  Current.  A  current  that  flows  in  the  one  direc- 
tion. Written  D.  C. 

Alternating  Current.  A  current  that  changes  its  flow 
of  direction  so  many  times  a  second  according  to  the 
construction  of  the  alternator.  Written  A.  C. 

Conductor.  Anything  that  will  permit  the  passage  of 
electricity.  A  wire. 

Rubber  Covered  Wire.  A  cable  either  solid  or  stranded 
with  a  rubber  covering  and  an  outer  protective  cover- 
ing of  cotton  braid.  Used  for  mains  for  motion  picture 
work. 


2  MOTION     PlCTtTRE      PROJECTION 

Asbestos  Covered  Wire.  A  cable  containing  very  fine 
strands  of  copper  wire  all  twisted  together  and  covered 
with  an  asbestos  covering.  Used  wherever  heat  is  gen- 
erated. On  motion  picture  circuits  used  between  the 
table  switch  and  arc  lamp. 

Stage  Cable.  A  cable  containing  twin  conductors  each 
insulated  from  the  other  and  the  whole  thing  covered 
with  a  composition  covering.  Used  for  temporary 
purposes. 

B.  X.  Metal  tubing  containing  two  conductors,  each 
conductor  insulated  from  the  other  by  a  rubber  covering, 
and  both  wires  wrapped  with  a  composition  covering 
so  as  to  completely  fill  the  tubing. 

Ammeter.  An  instrument  used  in  your  circuit  to 
measure  the  flow  of  amperes.  Connected  in  series. 

Voltmeter.  An  instrument  used  in  your  circuit  to 
measure  the  pressure  or  voltage.  Connected  in  multiple. 

Laminated.    Made  up  of  a  number  of  thin  iron  sheets. 

Current  Frequency.  The  number  of  times  alternating 
current  changes  its  flow  of  direction  a  second.  The 
changes  are  called  cycles. 

Sixty  Cycle  A.  C.  This  is  when  every  part  of  the  cir- 
cuit is  60  times  positive  and  60  times  negative  every 
second.  The  current  changes  its  flow  of  direction  60 
times  a  second. 

Induction.  The  property  of  a  charged  body  on  A.  C. 
to  charge  a  neighboring  body  running  parallel  to  it 
without  any  tangible  form  of  connection. 


MOTION      PICTURE      PROJECTION  3 

Watt.  The  unit  of  power.  The  product  of  one 
ampere  and  one  volt. 

Kilowatt.  1,000  watts  (written  K.  W.)  or  1.34  horse 
power  as  746  watts  equal  one  horse  power. 

Circular  Mil.  The  unit  of  area.  A  mil  is  the  one- 
thousandth  part  of  an  inch  and  a  circular  mil  is  the 
area  of  a  circle  whose  diameter  is  one  mil.  The  cross 
section  of  wires  is  measured  by  circular  mils. 

Short  Circuit.  Two  wires  of  opposite  polarity  coming 
in  contact  with  each  other  without  any  controlling 
device. 

Ground.  Caused  by  the  connection  of  an  electrical 
conductor  to  a  conducting  medium  other  than  that  to 
which  it  belongs. 

Polarity.  Pertaining  to  the  two  opposite  poles  of  a 
circuit;  the  positive  and  negative. 

Transrerter.  A  motor  generator  set,  an  A.  C.  or  D.  C. 
motor  connected  to  a  D.  C.  generator. 

Secondary  Coil.  The  coil  of  a  transformer  in  which 
the  current  is  induced,  connected  to  the  lamp. 

Primary  Coil.  The  coil  of  a  transformer  that  is  con- 
nected to  the  source  of  supply. 

Inductor.    A  step-down  transformer. 
Economizer.    A  step-down  transformer. 

Converter.  An  apparatus  used  to  change  A.  C.  to 
D.  C.  or  D.  C.  to  A.  C. 

Step-Down  Transformer.  A  transformer  that  steps 
down  the  voltage  and  raises  the  amperage. 


4  MOTION      PICTURE      PROJECTION 

Step-Up  Transformer.  A  transformer  that  steps  up 
the  voltage  and  lowers  the  amperage. 

Arc  Rectifier.  An  apparatus  used  to  change  A.  C. 
to  D.  G. 

Auto  Transformer.  A  transformer  provided  with 
only  one  coil  instead  of  two.  Part  of  the  coil  being 
traversed  by  the  primary  circuit  and  part  being  trav- 
ersed by  the  secondary  circuit. 

Dimmer.  An  adjustable  rheostat  for  increasing  or 
decreasing  the  resistance  in  an  incandescent  lamp 
circuit. 

Insulation.  Any  material  of  high  resistance  through 
which  electric  current  cannot  pass.  Rubber,  mica, 
glass  and  porcelain  are  all  insulating  materials. 

Lug.  A  wire  terminal.  These  lugs  should  always 
be  soldered  on  the  end  of  the  wires  except  when  such 
wires  are  to  be  used  where  heat  is  generated.  A  special 
lug  is  used  under  these  conditions  which  is  tightened 
on  wire  by  the  pliers.  No  solder  should  be  used  on  lugs 
that  are  used  on  the  rheostat  or  in  lamp  house. 

Watt  Hour.  The  amount  of  work  done  by  one  ampere 
at  a  pressure  of  one  volt  in  one  hour. 

Ampere  Hour.  The  amount  of  amperes  flowing  mul- 
tiplied by  the  time  in  hours.  One  ampere  flowing  for  one 
hour  equals  one  ampere  hour.  Two  amperes  flowing 
for  one-half  hour  equals  one  ampere  hour.  One-half 
ampere  flowing  for  two  hours  equals  one  ampere  hour. 

Coulomb.  The  amount  of  amperes  passing  in  a 
second.  The  product  of  amperes  times  seconds. 


MOTION      PICTURE      PROJECTION  5 

Knife  Switch.  A  switch  with  knife-like  blades  used 
on  circuits  carrying  heavy  currents. 

Negative.  A  term  used  to  denote  the  pole  of  a  source 
of  electricity  where  the  current  enters. 

Safety  Plug.  A  metal  plug  which  is  readily  fusible 
when  an  abnormal  current  passes,  used  as  a  safety 
device. 

Negative  Pole.  The  terminal  of  a  source  of  electricity 
at  which  the  current  enters  after  having  passed  through 
the  external  circuit. 

Positive  Pole.  The  terminal  from  which  the  current 
seems  to  start  in  traversing  the  external  circuit. 

Series.  An  arrangement  or  connection  of  electrical 
devices  in  a  circuit  so  that  the  current  will  pass  suc- 
cessively from  one  to  the  next  and  so  on  through  all,  as 
distinguished  from  a  parallel  or  multiple  arrangement, 
in  which  each  device  is  connected  directly  to  the  mains, 
or  terminals  of  the  source  of  supply  instead  of  being 
connected  thereto  through  the  other  devices. 

Insulating  Tape.  A  ribbon  of  some  flexible  material 
impregnated  with  rubber  or  other  suitable  non- 
conductor and  used  for  insulating  wires,  joints  and 
exposed  places. 

Positive  Wire.  The  wire  connected  with  the  positive 
pole  of  a  dynamo. 

Negative  Wire.  The  wire  by  which  a  current  returns 
to  its  source  after  completing  the  circuit. 

Induced  Current.  The  current  produced  in  a  con- 
ductor by  cutting  magnetic  lines  of  force. 


6  MOTION      PICTURE      PROJECTION 

Graphite.  A  soft  variety  of  carbon,  sometimes  -used 
for  lubrication. 

Alternator.  The  name  commonly  given  to  an  alter- 
nating current  dynamo. 

Armature.  The  part  of  the  dynamo  in  which  the 
current  is  induced,  and  which  may  be  either  stationary 
or  moving.  It  is  placed  near  the  poles  of  the  field 
magnet.  The  armature  proper  of  a  dynamo  is  usually 
a  mass  of  iron  upon  which  are  wound  coils  of  insulated 
wire. 

Armature  Core.  The  mass  of  iron  or  other  magnetiz- 
ing material  upon  which  the  coils  of  an  armature  are 
wound. 

Switch  Board.  A  board  provided  with  switches  which 
open,vclose,  or  interchange  circuits. 

Wheatstone  Bridge.  A  device  for  measuring  resistance. 

Dynamo  Brush.  Strips  of  metal  or  a  plate  of  metal 
or  of  carbon  which  bears  upon  the  commutator  of  a 
dynamo  and  takes  off  the  current  to  the  circuit. 

Brush  Holder.  A  device  for  holding  the  brush  of  a 
dynamo  or  motor  in  position. 

Commutator.  That  part  of  the  dynamo  or  motor 
which  changes  the  direction  of  the  current.  In  a 
dynamo  the  current  in  a  given  section  of  the  armature 
alternates,  and  must  be  made  continuous  on  leaving 
it.  This  is  done  by  the  commutator,  which  consists  of 
insulated  metal  bars  connected  with  the  armature 
wires  and  placed  so  as  to  feed  into  different  brushes  as 
the  current  changes. 


MOTION      PICTURE      PROJECTION  7 

Transforming  a  Current.  Changing  the  electric 
motive  force  of  a  current  by  its  passage  through  a  con- 
verter or  transformer. 

Efficiency  of  Dynamo.  The  total  electric  energy 
developed  by  a  dynamo,  divided  by  the  total  mechani- 
cal energy  required  to  drive  the  dynamo. 

Electric  Efficiency.  The  useful  electrical  energy  from 
any  source,  divided  by  the  total  consumed  energy. 

Magnetic  Field.  The  region  of.  magnetic  influence 
surrounding  the  poles  of  a  magnet. 

Filament.  In  an  incandescent  lamp  the  thread  of 
wire  or  carbon  which  becomes  luminous  under  the 
heating  effect  of  an  electric  current  passing  through  it. 

Magnetic  Force.  The  force  which  causes  the  attrac- 
tions or  repulsions  of  magnetic  poles. 

Horse  Power.  (Written  H.  P.)  A  commercial  unit 
for  power  or  rate  of  doing  work.  A  rate  of  doing  work 
equal  to  raising  550  Ibs.  one  foot  in  one  second,  or  33,000 
Ibs.  one  foot  in  one  minute,  always  involves  the 
three  factors,  force,  distance  and  time.  An  electrical 
horse  power  is  746  watts. 

Leads.  The  conductors  used  in  any  system  of  electric 
distribution. 

Link'  Fuses.  Fuses  for  electric  circuits  formed  by 
link-shaped  strips  of  fusible  metals. 

Magnet.  A  body  possessing  the  quality  of  attracting 
or  repelling  other  bodies. 

Pole  Finding  Paper.  Paper  used  to  tell  the  negative 
from  the  positive  wire. 


8^ MOTION      PICTURE      PROJECTION 

Motor  Regulator.  An  adjustable  rheostat  used  to 
regulate  the  speed  of  the  motor. 

Speed  Regulator.  An  attachment  on  machine  (gen- 
erally a  friction  disc  arrangement)  used  to  regulate  the 
speed  of  machine  (not  the  speed  of  the  motor). 

Fuse.  A  safety  device  used  in  your  circuit  to  protect 
your  line. 

Dynamo  or  Generator.    Used  to  generate  electricity. 
Motor  Generator.    A  generator  driven  by  a  motor. 

Multiple.  Multiple  connection  is  when  each  lamp 
draws  its  own  supply  from  the  source  of  supply,  and  is 
not  depending  on  any  other  lamp  or  set  of  lamps  for 
supply. 


faW  COIL* 


of  -THE     lN-T£RlOf{    OF   A 
OR 


10  MOTION      PICTURE      PROJECTION 


Powers  Cameragraph  No.  6A 
Showing  film  threaded  through  machine 


MOTION      PICTURE      PROJECTION  11 


PARTS  ON  THE  HEAD  OF  MACHINE 

UPPER  MAGAZINE  CENTRIFUGAL  MOVEMENT 

LOWER  MAGAZINE  IDLERS 

UPPER  FIRE  TRAP  TENSION  SPRINGS 

LOWER  FIRE  TRAP  FILM  RUNNERS 

UPPER  FIRE  SHIELD  BALANCE  WHEEL 

LOWER  FIRE  SHIELD  TAKE-UP 

UPPER  SPROCKET  LENS 

LOWER  SPROCKET  GEARS 

INTERMITTENT  SPROCKET     SPINDLES 
INTERMITTENT  MOVEMENT  AUTOMATIC  SHUTTER 
FLICKER  OR  LIGHT  SHUTTER  FRAMING  DEVICE 
GATE  COOLING  PLATE 

PARTS  ON  LAMP  HOUSE 

ARC  LAMP  DOWSER 

CONDENSERS  SLIDE  CARRIER 

FIRE  PREVENTION  DEVICES  ON  MACHINE 

UPPER  MAGAZINE  UPPER  FIRE  SHIELD 

LOWER  MAGAZINE  LOWER  FIRE  SHIELD 

UPPER  FIRE  TRAP  AUTOMATIC  SHUTTER 

LOWER  FIRE  TRAP  COOLING  PLATE 


12  MOTION      PICTURE      PROJECTION 

Automatic  Shutter.  The  shutter  covering  the  film 
aperture  in  gate  of  machine  and  controlled  by  the 
centrifugal  or  governor  movement,  is  so  arranged  that 
the  shutter  will  remain  up,  so  long  as  the  machine  is  in 
motion,  but  should  the  machine  stop  for  any  reason 
then  the  shutter  falls  and  cuts  off  the  rays  of  light  from 
the  film  in  gate.  (A  fire  prevention  device.) 

Fire  Trap.  An  arrangement  of  rollers  on  the  upper 
and  lower  magazines  through  which  the  film  is  fed,  used 
to  prevent  the  flame,  in  case  of  fire,  from  entering  the 
magazines. 

Flicker  Shutter.  A  revolving  shutter  on  head  of 
machine  just  in  front  of  the  projection  lens,  its  use 
being  to  cut  off  the  rays  of  light  from  screen  while  the 
film  is  in  motion  in  gate. 

Cooling  Plate.  The  plate  around  the  film  aperture 
on  gate  which  protects  the  gate  itself  from  getting  over- 
heated from  the  rays  of  light  from  arc  lamp. 

Intermittent  Movement.  The  movement  that  drives 
the  intermittent  sprocket,  generally  a  four  in  one 
movement. 

Tension  Springs.  On  gate  of  machine,  used  to  give 
the  proper  tension  to  film  while  passing  aperture. 

Take-up.  Generally  consists  of  a  split  pulley  and 
tension  spring,  its  use  is  to  drive  and  control  the  speed 
and  tension  of  the  reel  taking  up  the  film  in  lower 
magazine. 

Governor  Movement.  The  movement  that  works  the 
automatic  shutter,  works  by  centrifugal  force. 


MOTION      PICTURE      PROJECTION 


13 


Framing  Device.  An  attachment  on  the  machine 
which  allows  the  operator  to  frame  the  picture  on 
screen. 

Condensers.  A  lens  or  set  of  lenses  used  to  gather 
the  rays  of  light  from  the  arc  lamp  and  bring  them  to  a 
fixed  point  of  focus  on  aperture  in  gate. 

Dowser.  On  front  of  lamp  house,  used  to  cut  off  the 
rays  of  light  from  the  head  of  machine. 

Back  Focal  Length  of  Lens.  The  distance  from  the 
back  of  the  lens,  to  the  film  in  the  gate,  while  the  film 
is  in  focus  on  the  screen. 


v*C< 

*£f?*f* 


\J 


r>  -"*- 

\    v^ 


Right  and  wrong  way  to  set  D.  C.  arc.     I.  Lower  carbon 

not  far  enough  forward.     II.  Correct  setting. 

III.  Lower  carbon  too  far  advanced 


14  MOTION      PICTURE      PROJECTION 


WORKING  PRINCIPLE  OF  ELEMENTARY 
PROJECTION  MACHINE 

By  turning  the  operating  crank  A,  counter  clockwise, 
the  main  shaft  J5,  is  driven  through  the  4  to  1  reduction 
chain  drive  D,  a  steady  turning  motion  being  caused  by 
the  fly  wheel  (7,  this  in  turn  operates  the  upper  steady 
feed  sprocket  E,  through  the  4  to  1  reduction  gear  F, 
thus  the  teeth  of  E  sprocket  which  mesh  with  the  per- 
forations in  the  film,  feed  the  film  at  a  constant  rate, 
the  film  being  held  against  E  by  pressure  roller  G.  A 
film  loop  or  length  of  loose  film  is  thus  maintained 
between  E  and  the  steady  drum  H.  The  film  is  fed 
past  the  film  gate  intermittently  by  the  intermittent 
sprocket  I,  operated  by  the  Geneva  movement  K,  the 
latter  producing  a  quick  quarter  turn  of  /,  followed  by 
a  relatively  long  rest  during  which  the  main  shaft  B 
makes  one  revolution.  The  barrel  shutter  Z,  by  a  2  to  1 
gear  with  the  main  shaft  and 'proper  timing,  operates 
to  cut  off  the  light  rays  from  the  screen  during  each 
movement  of  the  intermittent  sprocket  I,  and  to  admit 
the  light  during  the  intervals  that  I  remains  stationary. 
The  synchronous  operation  of  the  intermittent  sprocket 
and  the  shutter  is  very  clearly  shown  in  the  diagram. 
A  lower  steady  feed  sprocket  M,  which  operates  at  the 
same  speed  as  the  upper  sprocket  E,  maintains  a  lower 
feed  film  loop  N,  and  feeds  the  film  to  the  lower  reel  0. 
Because  of  the  increasing  diameter  of  the  roll  of  film 
due  to  winding  the  film  on  reel  0,  the  velocity  of  rota- 


MOTION      PICTURE      PROJECTION 


15 


UPPER  REE 
REEL  BOX 


UPPER  FEED 
FILM  LOOP, 


RREEL 
EL  BOX 


10 


MOTION      PICTURE      PROJECTION 


tion  of  0  must  be  allowed  to  vary;  this  is  accomplished 
by  means  of  the  belt  drive  P,  the  belt  permitting 
slippage  below  the  maximum  speed.  It  should  be 
carefully  noted  that  the  total  revolutions  made  by  each 
of  the  three  sprockets  E,  /,  and  M ,  is  the  same,  the  only 
difference  being  that  the  motion  of  E  and  M  is  constant 
while  that  of  I  is  intermittent. 


Showing  effect  of  arc  being  connected  upside  down 


MOTION      PICTURE      PROJECTION  17 


THE  INTERMITTENT  MOVEMENT 

PRELIMINARY  REMARKS 

Too  much  prominence  cannot  be  given  to  the  inter- 
mittent movement  of  Power's  Cameragraph.  Before 
entering  into  a  technical  description  of  this  movement, 
it  will  be  well  to  give  a  brief  outline  of  the  fundamental 
principles  upon  which  the  art  of  moving  picture  pro- 
jection depends.  An  understanding  of  these  principles 
will  enable  one  to  better  appreciate  the  very  important 
part  that  Power's  Cameragraph  has  played  in  the  evo- 
lution of  the  moving  picture. 

The  moving  picture  is  accomplished  by  flashing  a 
great  number  of  stationary  photographic  views  before 
the  eye  in  such  rapid  succession  that  the  eye  is  deceived 
into  the  belief  of  having  beheld  actual  motion. 

The  photographic  views,  which  are  usually  taken  at 
the  rate  of  sixteen  per  second,  are  printed  in  direct  suc- 
cession upon  a  ribbon  of  transparent  film  one  and 
three-eighths  inch  in  width  and  between  one  and  two 
thousand  feet  in  length.  Each  view  is  condensed  into 
a  rectangular  space  approximately  one  inch  wide  and 
three-fourths  inch  high. 

When  the  film  is  run  through  the  projector  at  normal 
speed,  sixteen  of  these  views  are  shown  each  second. 
It  would  appear  from  this  that  each  view  is  shown  for 
one-sixteenth  of  a  second.  Such  is  not  the  case,  how- 
ever. Each  view  is  held  stationary  before  the  lens  for 
only  a  part  of  this  minute  period  of  time,  and  the 


18 


MOTION      PICTURE      PROJECTION 


remainder  of  the  period  is  consumed  while  the  film  is 
being  moved  down  a  distance  of  three-fourths  of  an  inch, 
so  as  to  bring  the  succeeding  view  in  line  with  the  lens. 


Figure  1 

During  every  such  movement  of  the  film,  the  main 
blade  (or  wing)  of  a  revolving  shutter,  passes  in  front 
of  the  lens,  thus  preventing  any  trace  of  the  movements 
from  reaching  the  screen.  If  this  was  not  done,  the 
picture  would  be  greatly  marred  by  streaks  of  light 
known  as  " travel  ghost."  An  additional  wing  (and 
sometimes  two)  is  inserted  in  the  shutter  wheel  for  the 


MOTION      PICTURE      PROJECTION 


19 


purpose  of  doing  what  is  technically  known  as  "equal- 
izing the  light."  We  will  not  discuss  this  matter  of 
light  equalization  as  it  has  no  direct  bearing  upon  the 
point  that  we  wish  to  bring  out. 

It  is  the  necessary  passage  of  these  wings  in  front  of 
the  lens  that  prevents  an  attainment  equalling  theo- 


Figure  a 

retical  perfection  wherein  each  view  would  appear  on 
the  screen  for  its  entire  allotment  of  one-sixteenth  of  a 
second  without  interruption  of  any  kind. 

It  would  probably  be  possible  to  devise  a  way  to 
move  the  film  so  rapidly  that  the  eye  could  not  perceive 
any  trace  of  the  movement,  and  thus  the  necessity  of 
using  the  revolving  shutter  would  be  eliminated,  but 
we  are  prevented  from  doing  this  by  the  very  important 
fact  that  wear  and  tear  on  the  film  must  be  taken  into 


20 MOTION     PICTURE      PROJECTION 

consideration.  The  movement  of  the  film  must  not  be 
made  so  rapidly  nor  in  such  a  jerky  manner  as  to  cause 
the  film  to  rip  or  pull  apart. 

Power's  Cameragraph  accomplishes  this  movement 
more  rapidly  than  any  other  projector  now  in  practical 
use.  The  nature  of  the  movement  is  such  as  to  keep 
wear  and  tear  on  the  film  reduced  to  a  minimum.  The 
mechanical  parts  which  control  the  movement  are  of 
greater  durability  than  those  used  in  any  other  pro- 
jector. These  great  advantages,  which  are  to  be  had 
only  with  Power's  Cameragraph,  have  done  their  full 
share  in  placing  this  projector  in  its  present  preeminent 
position  as  the  leader  in  the  art  of  picture  projection. 

TECHNICAL  DESCRIPTION  OF  THE 
INTERMITTENT  MOVEMENT 

The  term  "intermittent  movement"  is  used  to  desig- 
nate that  part  of  the  mechanism  of  a  moving  picture 
projector,  which  performs  the  important  function  of 
stopping  the  film  at  regular  intervals,  so  that  the  photo- 
graphic views  may  be  successively  held  in  line  with 
the  lens. 

In  Power's  Cameragraph  this  movement  consists 
primarily  of  four  elements,  namely :  a  diamond  shaped 
cam,  a  locking  ring,  a  pin  cross  and  a  sprocket.  Photo- 
graphic views  of  these  parts  will  be  found  on  page  18. 

The  cam  and  locking  ring  are  formed  together  on  the 
face  of  a  solid  steel  disc.  The  four  pins  of  the  pin  cross 
are  formed  from  the  end  of  a  solid  cylinder  of  steel. 
The  remainder  of  this  cylinder  is  turned  down  to  the 
proper  diameter  to  act  as  a  spindle  upon  which  the 
sprocket  is  securely  fastened.  The  sprocket  has  two 


MOTION      PICTURE      PROJECTION 


21 


rows  of  teeth  to  mesh  with  the  holes  that  are  perfor- 
ated on  each  side  of  the  film. 

Figures  a,  6,  c,  and  d,  show  these  elements  in  action. 
A  portion  of  the  back  of  the  cam-ring  disc  has  been 
cut  away  so  as  to  expose  the  workings  of  the  movement 
during  one  revolution  of  the  disc.  The  curved  arrows 


Figure  b 

indicate  the  direction  in  which  the  parts  are  revolving. 
The  sprocket  is  in  mesh  with  a  short  strip  of  film. 
Portion  e  of  this  film,  which  lies  between  the  heavy 
black  cross  lines,  represents  one  of  the  photographic 
views  to  be  projected  upon  the  screen. 

In  Figure  a,  the  four  pins  of  the  pin  cross  are  shown 
in  engagement  with  the  locking  ring.  Pins  1  and  2  are 
at  the  outer  circumference  and  pins  3  and  4  are  at  the 
inner  circumference  of  the  ring.  Although  the  ring  is 


22 


MOTION      PICTURE      PROJECTION 


revolving,  it  cannot  impart  motion  to  the  pin  cross  as 
the  pins  are  securely  locked  by  contact  with  the  inner 
and  outer  surfaces  of  the  ring;  consequently  the  pin 
cross,  the  sprocket  and  the  film  are  at  rest.  It  is  during 
this  period  of  rest  that  the  photographic  view  is  being 
projected  on  the  screen. 


Figure  c 

In  Figure  6,  the  pins  are  disengaging  from  the  locking 
ring.  The  cam  is  just  starting  to  engage  with  pin  1. 
As  the  engagement  takes  place  the  pin  is  pushed  for- 
ward and  upward,  thus  imparting  a  rotary  motion  to 
the  pin  cross  spindle.  The  sprocket,  being  fastened  to 
this  spindle  rotates  with  it,  thus  pulling  the  film 
downward. 

In  Figure  c,  pin  1  has  almost  reached  the  apex  of  the 
cam.  Pin  2  is  traveling  into  slot  /,  pin  3  is  describing 


MOTION      PICTURE      PROJECTION 


23 


an  arc  in  the  space  between  the  ends  of  the  locking  ring, 
and  pin  4  is  traveling  out  of  slot  g.  As  pin  1  slides  over 
the  apex  of  the  cam,  pin  4  engages  with  the  curved 
surface  h  at  the  end  of  the  locking  ring,  and  the  pin  is 
thrown  forward  and  upward  until  it  slides  on  to  the 
outer  surface  of  the  locking  ring. 


Figure  d 

In  Figure  d,  pin  4  has  just  reached  the  outer  surface 
of  the  ring.  The  four  pins  are  immediately  locked  as 
the  locking  ring  travels  into  the  space  between  them. 
In  contrast  to  the  pin  position  in  Figure  cr,  pins  1  and  4 
are  now  at  the  outer  circumference  and  pins  2  and  3 
are  at  the  inner  circumference  of  the  locking  ring.  It 
can  readily  be  seen  that  the  pin  cross  spindle  has  made 
a  quarter  revolution,  and  that  view  <?,  has  been  drawn 
downward  a  corresponding  distance. 


24 MOTION     PICTURE     PROJECTION 

Bear  in  mind  that  these  pins  can  only  move  in  the 
path  of  a  circle.  As  pins  2  and  4  travel  through  their 
respective  slots  it  would  appear  to  the  uninitiated  mind 
as  though  the  pins  must  travel  in  a  straight  line.  This 
is  not  the  case  however.  The  fact  that  the  cam-ring 
disc  is  revolving,  constantly  changes  the  position  of 


these  slots  so  that  their  straight  lines  intersect  the  cir- 
cular path  of  the  pins  at  successively  different  points. 

One  great  advantage  that  this  particular  movement 
has  to  offer,  may  be  demonstrated  by  making  the  fol- 
lowing simple  experiment: 

Tie  a  one  foot  length  of  ordinary  cotton  thread  to  a 
piece  of  metal  weighing  slightly  over  one  pound.  Take 
the  untied  end  of  the  thread  between  the  fingers  and  by 
an  upward  pull,  endeavor  to  lift  the  piece  of  metal  a 
distance  of  one  foot  in  the  shortest  possible  time.  A 


MOTION      PICTURE      PROJECTION 


25 


sudden  jerk  will  snap  the  thread.  A  slow  upward  pull 
will  allow  the  thread  to  stand  the  strain  of  the  weight, 
but  considerable  time  is  consumed  in  lifting  the  metal. 


Intermittent  movement  with  oil  tight  casing 

If  the  slow  pull  is  exerted  until  the  metal  has  started  to 
move,  the  pull  may  then  be  steadily  increased,  and 
consequently  the  metal  can  be  lifted  much 
quickly. 


more 


26  MOTION      PICTURE      PROJECTION 

This  analogy  may  be  applied  to  the  intermittent 
movement  of  Power's  Cameragraph,  which  has  been 
carefully  designed,  to  move  the  film  downward,  by 
starting  the  motion  with  a  scarcely  perceptible  pull 
that  steadily  increases  to  a  maximum  as  pin  1,  (Figure 
c)  slides  over  the  apex  of  the  cam,  after  which  it  de- 
creases in  the  same  steady  manner  until  the  pins  are 
locked  by  the  ring,  and  the  film  is  again  at  rest.  Not  a 
moment  of  time  is  lost,  and  yet  the  film  is  moved  so 
easily  that  the  wear  and  tear  is  reduced  to  a  minimum. 

The  elements  of  the  intermittent  movement  are 
made  from  carefully  selected  tungsten-chromium  steel, 
which  is  very  tough  and  durable.  The  most  delicate 
instruments  are  used  in  measuring  the  dimensions  of 
the  elements,  one  ten-thousandth  of  an  inch  plus  or 
minus  being  the  limit  of  permissible  variation. 

The  cam  and  pin  cross  are  enclosed  in  an  oil-tight 
casing.  An  oil  cup  is  fastened  to  this  casing,  and  by 
keeping  the  parts  plentifully  supplied  with  a  high  grade 
machine  oil,  a  practically  noiseless  operation  of  the 
movement  without  perceptible  wear  on  the  parts,  is 
insured. 

This  movement  has  been  used  exclusively  in  Power's 
Cameragraph  for  over  nine  years.  It  has  withstood 
every  test  of  time,  until  today  it  is  recognized  in  the 
motion  picture  industry  as  representing  durability, 
serviceability  and  dependability. 


MOTION      PICTURE      PROJECTION 


27 


THE  GENEVA  INTERMITTENT 

Diagram  showing  progressively  the  operation  of  the 
Geneva  intermittent  movement:  Figure  1  shows  the 
approach  of  pin;  Figure  2,  initial  position  or  beginning 
of  movement;  Figure  3,  mid-position;  Figure  4,  final 
position  or  end  of  the  movement;  Figure  5,  recession  of 
pin ;  Figure  6,  mid-position  of,  stationary  period. 

The  Geneva  movement  consists  of  a  maltese  cross 
M,  and  a  disc  S9  provided  with  a  pin  F,  and  a  circular 
guide  G. 

In  operation  the  pin  disc  *S  is  in  continuous  motion 
and  the  pin  is  so  located  that  it  enters  one  slot  of  the 
cross  M  and  carries  it  along  with  it,  thus  causing  one- 
quarter  revolution.  The  circular  guide  G  is  cut  away 
sufficiently  to  allow  the  cross  to  make  a  quarter  revolu- 
tion, but  when  it  registers  with  the  cross  it  holds  the 
latter  securely  until  the  pin  rotates  around  to  the 
next  slot. 


28 


MOTION      PICTURE      PROJECTION 


Simplex  Projector 


MOTION      PICTURE      PROJECTION 


29 


AUTOMATIC  SHUTTER 

The  shutter  covering  the  aperture  in  gate  of  machine 
and  controlled  by  the  centrifugal  movement.  It  is  so 
arranged  that  the  shutter  will  be  held  up  by  centrifugal 
force  as  long  as  the  machine  is  in  motion,  but  should 
the  machine  stop  for  any  reason  then  the  shutter  falls 
and  cuts  off  the  light  from  film.  It  is  a  fire  prevention 
device.  Should  the  automatic  shutter  refuse  to  work 
and  same  cannot  be  remedied  by  oiling,  it  will  then  be 
necessary  to  take  the  cover  off  the  centrifugal  move- 
ment Figure  624,  then  examine  springs  and  shoes 
Figure'^741,  and  see  if  the  shoe  track  Y  is  not  scratched. 


MOTION      PICTURE      PROJECTION  31 


ELECTRICITY 

No  one  knows  exactly  what  electricity  is,  we  do  not 
even  know  what  it  consists  of,  we  do  know  that  elec- 
tricity and  magnetism  are  one  and  the  same.  Elec- 
tricity is  not  matter  nor  yet  is  it  energy,  although  it 
is  a  means  of  transmitting  energy,  and  we  know  how 
to  handle  this  force  for  this  purpose. 

It  is  an  undeniable  fact  that  energy  cannot  be  created 
nor  can  it  be  destroyed,  but  we  can  convert  one  kind 
of  energy  into  energy  of  another  kind.  For  example, 
should  we  light  a  fire  under  a  vessel  containing  water 
we  will  convert  the  heat  energy  from  the  coals  to 
steam  energy  in  the  vessel  containing  the  water,  and 
we  could  again  change  this  steam  energy  into  me- 
chanical energy,  as  is  done  with  the  locomotive. 

It  is  also  possible  to  convert  mechanical  energy  into 
electrical  energy  so  by  connecting  the  mechanical 
energy  created  by  the  steam  to  a  dynamo  we  would 
produce  electrical  energy. 

It  is  also  possible  to  convert  electrical  energy  into 
mechanical  energy.  A  motor  is  used  for  this  purpose. 


ARC 


VOLTMETER     CONNECTED    IN    MULTIPLE 
AMMETER     CONNECTED    IN    SERIES 


32 


MOTION      PICTURE      PROJECTION 


MOTION      PICTURE      PROJECTION 


33 


34  MOTION     PICTURE     PROJECTION 

The  word  dynamo  is  used  to  designate  a  machine 
which  produces  direct  current  as  distinguished  from 
the  alternator  or  generator  which  produces  alternating 
current.  A  dynamo  does  not  create  electricity  but 
produces  an  induced  electric-motive  force  which  causes 
a  current  of  electricity  to  flow  through  a  circuit  of  con- 
ductors in  much  the  same  manner  as  a  pump  causes 
water  to  flow  through  a  pipe.  The  point  to  be  settled 
in  the  minds  of  those  taking  up  electricity  is  that  the 
dynamo  merely  sets  into  motion  something  already 
existing,  by  generating  sufficient  pressure  to  overcome 
the  resistance  to  its  movement. 

Although  we  speak  of  alternating  and  direct  current, 
it  should  be  clearly  understood  that  it  is  impossible  to 
get  a  continuous  current  with  a  dynamo.  The  current 
is  really  a  pulsating  one,  but  the  pulsations  are  so  small 
and  follow  each  other  so  quickly  that  the  current  is 
practically  continuous. 

Resistance.  The  property  of  anything  in  an  electric 
circuit  which  will  resist  the  flow  of  current.  Can  be 
compared  to  the  resistance  offered  to  the  flow  of  water 
through  a  pipe,  by  the  friction  created  by  the  sides  of 
the  pipe.  The  effect  of  resistance  is  to  produce  heat. 
Everything  in  the  circuit  offers  resistance.  The  re- 
sistance of  all  wires  increases  as  the  diameter  of  the 
wire  is  made  less,  or  as  its  length  is  increased.  The 
resistance  decreases  if  the  wire  is  made  larger  (cross 
section)  or  is  decreased  in  length. 

The  resistance  of  all  metals  increases  with  an  in- 
crease of  temperature. 

The  resistance  of  all  carbons  and  insulating  material 
decreases  with  an  increase  of  temperature. 


MOTION      PICTURE      PROJECTION  35 

Resistance  consumes  pressure. 

To  find  the  resistance  offered  by  a  copper  wire, 
multiply  its  length  in  feet  by  10.5  and  divide  the 
product  by  the  area  of  wire  in  circular  mils. 

Ohms  Law.  Ohms  law  is  merely  the  fundamental 
principal  on  which  most  of  electrical  mathematics  are 
worked. 

A  series  of  formulas  used  by  electricians  in  figuring 
voltage,  amperage  and  resistance: 

FORMULA  1.    To  find  the  amount  of  current  flowing  in  a  circuit 
divide  the  voltage  by  the  resistance,  or 

Electric  Motive  Force 

Current^ — — ; 

Resistance 

For  instance,  if  we  have  a  line  voltage  of  100  and 
our  circuit  has  a  resistance  of  5  ohms,  then  by  di- 
viding 100  by  5,  we  would  get  our  amperage. 

5  )  100  (  20 
100 

so  we  would  have  20  amperes. 

FORMULA  2.    To  find  the  amount  of  resistance  in  a  circuit,  divide 
the  voltage  by  the  amount  of  amperage  drawn,  or 

Electric  Motive  Force 


Resistance  = 


Current 


For  instance  suppose  we  have  a  line  voltage  of  100 
and  are  using  20  amperes  at  arc  lamp,  then  by  di- 
viding the  100  by  20  we  would  get  the  amount  of 
resistance  we  have  in  our  circuit. 

20  )  100  (  5 
100 

so  we  would  have  5  ohms  resistance  in  our  circuit. 


36 


MOTION      PICTURE      PROJECTION 


FORMCTLA  3.    To.find  the  voltage  of  a  circuit,  multiply  the  amount 
of  amperes  drawn  by  the  amount  of  resistance,  or 

Electric  Motive  Force  —  Amperes  times  Resistance 

For  example:  If  we  had  20  amperes  at  arc  and 
our  circuit  was  offering  5  ohms  resistance,  then  by 
multiplying  20  by  5  we  would  get  our  voltage. 

20  amperes 
o  ohms 

100  volts 

To  find   Volts.      Multiply   number   of    Amperes   by   amount   of 

Resistance. 

To  find  Resistance.    Divide  Voltage  by  Amperage. 
To  find  Amperage.    Divide  Voltage  by  Resistance. 

To  find  Watts.    Multiply  Voltage  by  Amperage. 
To  find  Amps.    Divide  Watts  by  Volts. 
To  find  Volts.    Divide  Watts  by  Amperage. 


MOTION      PICTURE      PROJECTION  37 


DYNAMOS 

A  dynamo  electric  machine  is  a  device  for  converting 
mechanical  energy  into  electric  energy.  The  word 
dynamo  is  generally  understood  to  mean  a  machine  for 
converting  mechanical  energy  into  electrical  energy, 
and  the  word  motor  means  a  machine  for  converting 
electric  energy  into  mechanical  energy,  the  essential 
parts  of  a  dynamo  and  motor  are  the  same,  namely— 
the  armature  and  field  magnet. 

Dynamos  are  divided  into  two  general  classes,  ac- 
cording to  the  character  of  the  current  they  deliver. 
A  direct  current  dynamo  delivering  a  current  that 
always  flows  in  the  one  direction,  that  is,  the  current 
never  reverses,  though  it  may  change  in  value  or  pulsate. 


100   K.W.    ENGINE-TYPE    GENERATOR   AND   AUTOMATIC   HIGH-SPEED   ENC'VB. 


38 


MOTION      PICTURE      PROJECTION 


Alternating  current  dynamos  or  alternators,  deliver  a 
current  that  periodically  reverses  its  direction  of  flow,  the 
number  of  reversals  per  second  depending  on  the  num- 
ber of  poles  in  the  dynamo  and  on  the  speed  of  rotation. 

A  direct  current  dynamo  usually  consists  of  a  series 
of  conductors  arranged  on  the  surface  of  a  cylindrical 
iron  core  or  in  slots  near  the  surface,  the  conductors  in 
most  cases  being  parallel  with  the  axis  of  the  core. 

The  core  is  mounted  on  a  shaft  that  is  supported  on 
bearings  so  that  the  armature  can  be  rotated  near  the 
pole  faces  of  a  field  magnet.  This  magnet  is  excited  by 
one  or  more  field  coils.  Any  even  number  of  poles  may 
be  used  according  to  the  size  and  type  of  machine. 

The  principal  parts  of  a  dynamo  are:  armature  core, 
bands  on  armature  core,  commutator,  shaft,  field  coils, 
pole  faces,  brushes,  rear  end  bearing,  front  end  bearing, 
rear  end  journal,  front  end  journal,  terminal  block  and 
bedplate. 


LINE  rusEs 
j  15  AM  PS.  FOR  HO  VOLTS 

•  220 

•  550 


CURRENT  AT  ARC 
IS  ADJUSTABLE 

FROM  2O  TO 
35AMPS. 


MOTION      PICTURE      PROJECTION 


39 


THE  RHEOSTAT 

The  rheostat  is  an  instrument  or  device  introduced 
into  your  circuit  to  offer  resistance  and  thereby  reduce 
the  line  voltage. 

A  rheostat  is  made  of  a  number  of  metal  coils  or 
plates  connected  in  series  and  mounted  on  an  insulated 
frame,  and  covered  with  a  perforated  metal  cover. 

Rheostats  may  be  connected  in  series  or  multiple 
with  each  other  but  must  always  be  connected  in  series 
with  the  arc. 

Rheostats  are  sometimes  spoken  of  as  resistance 
boxes,  they  can  be  used  on  either  alternating  or  direct 
current,  although  it  is  more  economical  to  use  a  trans- 
former on  alternating  current  instead. 

The  same  rheostat  will  pass  about  10%  more  amper- 
age on  A.  C.  than  on  D.  C.,  the  reason  being  that  with 
an  A.  C.  arc  you  must  feed  the  carbons  a  little  closer 
together  and  this  will  draw  more  amperage. 

By  connecting  two  rheostats  in  series  their  total 
resistance  will  be  added.  For  instance  if  we  connected 
two  rheostats  each  offering  4  ohms  resistance,  in  series 


RHE.OSTAT5  IN  MULTIPLE 


40 


MOTION      PICTURE      PROJECTION 


with  each  other  we  would  then  have  a  total  resistance 
of  8  ohms  on  our  line.  By  connecting  the  same  two 
rheostats  in  multiple  with  each  other  we  would  only 
have  approximately  2  ohms  resistance  in  our  line. 

Never  connect  110  volt  rheostats  either  singly  or  in 
multiple  on  a  220  volt  circuit  because  by  so  doing  you 
will  burn  out  the  coils.  However  it  is  possible  to  use 
two  110  volt  rheostats  connected  in  series  with  each 


ARC 


RHEOSTATS     IN     SERIES 


other  on  220  volts  although  they  would  be  a  trifle 
overloaded  and  should  only  be  used  till  such  time  as 
a  220  volt  rheostat  can  be  obtained. 

The  point  must  never  be  lost  sight  of  that  rheostats 
are  very  wasteful,  the  electrical  energy  is  converted 
into  heat  energy  which  goes  to  waste,  but  which  is  of 
course  registered  on  the  meter  and  has  to  be  paid  for. 

Rheostats  are  considerably  less  than  50%  efficient. 

All  connections  in  a  rheostat  should  be  kept  tight 
and  the  lugs  and  leads  attached  to  the  binding  posts  of 
rheostats  should  be  removed  every  so  often  as  it  will  be 
found  that  both  the  leads  and  lugs  have  lost  their 
nature  through  the  excessive  heat.  This  also  applies 
to  the  lugs  and  asbestos  leads  in  the  arc  lamp. 
f  Should  a  coil  burn  out  while  you  are  operating,  the 
rheostat  can  be  patched  up  for  the  time  being,  by  dis- 


MOTION      PICTURE      PROJECTION 


41 


connecting  the  short  length  of  the  coil  and  stretching 
the  other  part  of  broken  coil  till  same  can  be  screwed 
in  place. 

Rheostats  should  always  be  placed  outside  the  booth, 
it  will  reduce  the  fire  risk,  and  it  will  be  a  lot  more 
comfortable  for  the  operator. 


Power's  rheostat  with  cover  removed 
showing  connection  of  coils 


42 


MOTION      PICTURE      PROJECTION 


THE  TRANSFORMER 

• 

The  transformer  is  an  apparatus  used  on  alternating 
current  in  place  of  a  rheostat. 

A  transformer  is  made  of  two  copper  coils  the  primary 
and  secondary  and  a  laminated  iron  core.  The  current 
enters  through  the  primary  coil  and  the  action  of  the 
current  (A.  C.)  sets  up  in  the  transformer  a  magnetic 
field  around  the  iron  core,  the  secondary  coil  cuts  the 
lines  of  magnetic  force  and  carries  off  the  new  magne- 
tized current  to  the  arc  lamp. 

The  current  gets  from  the  primary  to  the  secondary 
coil  by  induction,  there  is  no  metallic  connection  between 
the  two,  in  fact  the  coils  are  insulated  from  each  other 
and  from  the  iron  core. 

There  are  two  kinds  of  transformers:  step-up  trans- 
formers and  step-down  transformers.  The  step-up 


I  WALL 
SWITCH 


TRANSFORMER 
CONNECTIONS 
FOR    M.P.WORK 


MOTION     PICTURE     PROJECTION  43 

transformers  steps  up  the  voltage  and  lowers  the 
amperage.  The  step-down  transformer  steps  down  the 
voltage  and  raises  the  amperage.  It  is  always  the 
step-down  that  is  used  in  connection  with  motion 
picture  work. 

The  wattage  on  the  primary  coil  is  always  larger 
than  on  the  secondary  coil,  that  is,  the  input  is  greater 
than  the  output  in  watts.  This  is  due  to  the  losses  in 
transforming  the  current.  The  losses  are  divided  into 
two  classes: 

(a)  The  iron  or  core  losses. 
(6)  The  copper  losses. 

The  core  losses  are  going  on  as  long  as  the  switch 
on  the  line  side  of  transformer  is  closed,  in  other  words 
while  the  transformer  is  carrying  a  no-load  current. 

The  copper  losses  take  place  only  while  the  arc  is 
burning  or  current  is  being  drawn  from  the  secondary 
coil. 

An  auto-transformer  is  a  transformer  with  one  coil 
only,  part  of  the  coil  being  traversed  by  the  primary 
circuit  and  part  by  the  secondary  circuit. 

Mica  is  the  most  efficient  insulation  for  transformers. 

Transformers  are  known  under  many  trade  names 
such  as  economizers,  inductors,  etc. 

By  installing  a  transformer  in  place  of  a  rheostat 
on  a  110  volt  alternating  current  system  the  makers 
claim  there  is  a  saving  of  about  66%. 

Transformers  are  about  95%  efficient. 


44  MOTION      PICTURE      PROJECTION 


CARBONS 

Carbons  are  made  in  different  lengths  and  different 
sizes  in  cross  section,  it  is  necessary  that  you  use  the 
proper  combination  of  carbons  to  secure  best  results 
on  screen.  On  110  volts  D.  C.  up  to  35  amperes  use  5-8 
cored  in  top  (positive)  and  1-2  solid  in  bottom  (nega- 
tive), from  35  to  60  amperes  use  3-4  cored  in  top 
(positive)  and  5-8  solid  in  bottom  (negative)  from  60  to 
80  amperes  use  7-8  cored  in  top  and  5-8  solid  in  bottom. 

On  A.  C.  using  up  to  35  amperes  at  arc  use  5-8  cored 
for  top  and  bottom,  from  35  to  60  amperes  3-4  cored 
top  and  bottom,  from  60  up  to  80  amperes  use  7-8  top 
and  bottom. 

The  resistance  of  carbons  decreases  with  an  increase 
of  temperature. 

Store  your  carbons  in  a  dry  place. 

See  that  carbons  make  good  contact  in  jaws  of  arc 
lamp.  . 


MOTION     PICTURE      PROJECTION  45 


THREE  WIRE  SYSTEM 

A  system  of  wiring  where  three  instead  of  two  sets 
of  two  wires  are  used,  generally  obtained  by  connecting 
two  dynamos  in  series  and  connecting  a  third  or  neutral 
wire  to  a  point  common  to  both  dynamos.  The  wires 
are  positive,  negative  and  neutral.  The  advantage  of 
the  system  is  the  saving  of  copper.  The  disadvantages 
of  the  system  (aside  from  the  question  of  generation) 
are  that  the  switches,  etc.,  are  more  expensive,  and 
unless  the  system  is  kept  balanced  (the  same  amount 
of  amperage  being  drawn  off  both  sides  of  the  system) 
you  are  liable  to  damage  the  lamps  on  the  line. 

In  the  three  wire  system  two  dynamos  alike  in 
voltage  and  capacity  are  connected  in  series  between 
the  outside  wires,  and  the  neutral  wire  is  connected 
with  a  point  in  the  circuit  between  the  two  dynamos. 

Being  in  series  the  voltage  of  the  dynamos  are  added 
making  the  voltage  between  the  two  outside  wires 
double  that  between  the  neutral  (middle  wire)  and 
either  of  the  outside. 

The  lamps  are  connected  between  either  of  the  out- 
side wires  and  the  neutral  wire,  and  if  an  equal  number 
of  lamps  are  connected  on  each  side  (that  is,  if  the 


Fi 


46  MOTION      PICTURE      PROJECTION 

system  is  balanced)  there  will  be  no  flow  of  current  in 
the  neutral  wire. 

In  any  case,  the  amperage  in  the  neutral  wire  is  the 
difference  between  the  amperage  drawn  from  each  side. 
This  difference  should  be  kept  as  small  a*s  possible. 

Figure  1  shows  a  three  wire  system.  D  and  E  being 
two  110  volt  dynamos  connected  in  series,  A  is  the 
positive  wire,  B  the  neutral  wire,  and  C  the  negative 


-H.3        — »2 


wire.  The  ten  circles  on  either  side  of  the  neutral  wire 
represent  lamps  each  taking  one  ampere,  as  we  have 
the  same  amount  of  current  (10  amperes)  being  drawn 
off  either  side,  the  system  is  balanced  and  there  is  no 
flow  of  current  in  the  neutral  wire.  The  ten  amperes 
being  drawn  from  the  positive  wire  A,  and  returning 
to  the  dynamo  over  the  negative  wire  C. 

Figure  2  shows  an  unbalanced  three  wire  system. 

Taking  it  for  granted  that  each  of  the  lamps  is 
taking  one  ampere,  then  we  have  four  amperes  on  one 
side  and  six  amperes  on  the  other,  so  our  system  is 
unbalanced  to  the  extent  of  two  amperes,  which  repre- 
sents the  flow  of  current  in  the  neutral  wire.  Connected 
between  wires  A  and  C  we  would  have  220  volts,  or 
the  added  voltage  of  the  dynamos.  Connected  between 
A  and  B  or  between  B  and  C  we  would  have  110  volts. 


MOTION      PICTURE      PROJECTION  47 


THE  HALLBERG  ECONOMIZER        ^ 

The  Hallberg  economizer  is  §imply  a  transformer  of 
the  semi-constant  current  type,  taking  A.  C.  current 
at  line  voltage  and  delivering  A.  C.  current  at  arc 
voltage.  Semi-constant  means  that  it  will  take  the 
line  current  at  a  fixed  potential  and  will  deliver  from 
the  secondary  a  steady  amperage  flow  regardless  of 
the  length  of  the  arc. 

The  economizer  consists  of  a  continuous  rectangular 
core,  on  one  leg  of  which  is  the  primary  winding,  on  the 
opposite  core  leg  is  the  secondary  which  is  made  of 
larger  cross  section  wire,  this  coil  is  connected  to  lamp. 

On  110  volts  the  economizer  line  wires  are  usually 
attached  to  terminals  1  and  2  for  any  voltage  from 
100  to  105,  to  1  and  3  for  110  volts  or  to  1  and  4  for 
voltage  between  115  and  210.  See  diagram  on  page  48. 

Some  operators  desire  varying  candle  power  at  the 
arc  lamp  to  accommodate  lighter  or  more  dense  films, 
in  a  case  of  this  kind,  it  is  possible  to  simply  install  a 
three  pole  main  line  cut  out  (with  one  single  fuse  plug) 
connected  to  the  economizer  (see  diagram).  By  placing 
the  plug  in  socket  No.  2,  a  heavy  amperage  is  obtained, 
Unscrew  plug  and  place  in  3  and  we  get  a  medium 
current,  and  if  we  place  plug  in  4  we  get  the  lowest 
amperage  possible.  This  gives  us  three  degrees  of 
amperage  at  arc.  By  installing  more  than  one  fuse  at 
a  time  we  would  blow  the  fuse  as  this  would  be  short- 
circuiting  the  primary  coil. 


48 


MOTION      PICTURE      PROJECTION 


TO  LIKE 


PltfG 


When  using  the  Hallberg  economizer: 

1.  Place  economizer  at  least  12  inches  away  from 

sheet  iron  walls,  as  otherwise  there  will  be  a 
humming  noise. 

2.  30  amperes  line  fuses  is  large  enough  for  110  volts 

and  15  amperes  for  220  volts. 

3.  Connect   fuses,    switches   and   wires    exactly   as 

illustrated  on  page  49. 

4.  Make  sure  that  all  connections  are  tight,  especially 

at  the  carbon  clamps  in  the  lamp  house. 


MOTION      PICTURE      PROJECTION 


49 


5.  Cover    all    line    terminals    on    economizer    with 

tape. 

6.  Use  only  5-8  inch  soft  carbons  cored. 

7.  Feed  carbons  often  and  a  little  at  a  time. 

8.  Keep  arc  short,  not  over  1-32  inch. 


Showing  economizer  connections 
from  wall  switch  to  arc  lamp 


MOTION      PICTURE      PROJECTION  51 


CONVERTERS 

A  converter  is  any  piece  of  apparatus  for  changing 
electrical  energy  from  one  form  to  another. 

A  direct  current  converter  converts  from  D.  C.  to 
D.C. 

A  rotary  converter  converts  from  an  alternating 
current  to  a  direct  current. 

A  rotary  converter  combines  a  motor  and  generator 
having  but  one  field  and  one  armature  winding. 

EQUIVALENTS  OF  ELECTRICAL  UNITS 

1  kilowatt  =  1000  watts 

1  kilowatt  =  1.34H.P. 

1  kilowatt  =  44,257  foot  pounds  per  minute 

1  horse  power  =  746  watts 

1  horse  power  =  33,000  foot  pounds  per  minute 


Ammeter  — 


Adapting  HnKs  for 
fJ0<OK/22VViO/.t$Uppty 
Contact  as  shown  on. 

Z2O  trfttf  «7-S  per 
cfotfeaf  h'rtes  for  no 

High 


$w/tch  for  us/rigr* 
cither  AC.  or  '• 
O.C.Cft  the  Arc  \ 


ffequ fating  Dial 
~      Switch 


Mam  Reactance 


-ShaM/icf  Co// 
Starting  /f/toafe 


C/ip 


•* — Mam  f?eactanc& 


Front  and  back  view  of  mercury  rectifiers 


MOTION      PICTURE      PROJECTION 


53 


MERCURY  ARC  RECTIFIERS 

An  apparatus  used  to  change  A.  C.  to  D.  C. 
Consists  of  a  glass  bulb  into  which  are  sealed  two 
iron  anodes  and  one  mercury  cathode  and  a  small 
starting  electrode. 

The  bulb  is  filled  with  mercury  vapor.  No  current 
will  flow  till  the  starting  electrode  resistance  has  been 
overcome  by  the  conization  of  the  vapor  in  its  neigh- 
borhood. To  accomplish  this,  the  voltage  is  raised 
sufficiently  to  cause  the  current  to  jump  the  gap  be- 
tween the  mercury  cathode  and  the  starting  cathode, 
or  by  bringing  the  cathode  and  starting  electrode  to- 
gether in  the  vapor  by  tilting  and  then  separating  them, 

thus  drawing  out  the 
arc.  When  this  has 
been  done  current 
will  flow  from  the 
anode  to  the  mercury 
cathode  and  not  in 
the  reverse  direction. 
In  order  to  maintain 
the  action  a  lag  is 
produced  in  each  half 
wave  by  the  use  of  a 
reactive  or  sustaining 
coil,  hence  thecurrent 

Sents  Under 'coa 

woy  never  reaches  its  zero 
value  otherwise  the 
arc  would  have  to  be 
re-started. 


54 


MOTION      PICTURE      PROJECTION 


POWERS  INDUCTOR 

The  Powers  inductor  is  merely  a  step-down  trans- 
former. It  consists  of  two  copper  coils  wound  around 
an  iron  core  and  covered  with  a  perforated  metal 
covering,  two  wires  leave  the  front  which  is  marked 
lamp  and  the  two  that  leave  the  rear  are  connected  to 
the  source  of  supply.  It  is  of  the  adjustable  type  so 
that  it  is  possible  to  get  45  amperes  on  low,  55  when  on 


Powers  inductor  showing  adjusting  handle 


MOTION      PICTURE      PROJECTION 


55 


medium  and  65  on  high.  The  efficiency  rating  of  the 
Powers  inductor  will  compare  favorably  with  any 
transformer  on  the  market.  It  weighs  approximately 
100  pounds,  occupies  a  floor  space  of  12  x  14  inches 
and  is  19  inches  in  height.  Below  we  see  a  Powers 
inductor  connected  to  two  arc  lamps. 


Powers  inductor  connected  to  two  arc  lamps 


56  MOTION     PICTURE     PROJECTION 


CARE  OF  MOTOR 

The  motor  must  be  kept  clean,  if  the  commutator 
becomes  rough,  smooth  it  up  with  No.  00  sandpaper 
moistened  with  a  little  oil.  When  fitting  new  brushes 
always  sandpaper  them  down  to  fit  the  commutator 
perfectly  by  passing  to  and  fro  beneath  the  brushes 
a  strip  of  sandpaper  having  the  rough  side  of  paper 
towards  the.  brushes. 

Always  renew  brushes  before  they  get  too  short,  as 
should  the  brush  holders  come  in  contact  with  com- 
mutator great  damage  may  be  done. 

Keep  the  grease  cups  well  filled.  If  the  motor  gets 
overheated,  see  that  bearings  are  all  right;  see  that 
motor  is  lined  up  true. 

It  is  well  to  test  motor  every  now  and  again  with  a 
speed  indicator  to  see  that  you  are  getting  the  rated 
number  of  revolutions  per  minute.  Trouble  in  a  motor 
may  thus  sometimes  be  avoided. 

Sparking  at  commutator  may  be  laid  to  several 
faults,  among  them  being:  dirt,  uneven  brushes,  high 
mica,  broken  segment  in  commutator. 


MOTION      PICTURE      PROJECTION  57 


MEASURING  WIRE 

First  scrape  off  the  insulation,  then  take  one  strand 
of  wire  and  insert  it  in  the  smallest  slot  possible  on  a 
Brown  and  Sharp  wire  gauge.  Find  out  (by  using  wire 
table)  the  number  of  circular  mils  contained  in  the  one 
strand,  then  multiply  the  number  of  circular  mils  by 
the  number  of  strands  in  the  wire,  then  refer  to  wire 
table  and  find  the  nearest  corresponding  number  of 
circular  mils,  look  opposite  to  find  what  size  wire 
you  have. 

For  instance,  suppose  we  are  going  to  measure  a 
length  of  stranded  wire,  we  first  take  one  strand  and 
measure  with  B.  &  S.  gauge.  Let  us  take  it  for  granted 
that  it  measures  No.  14,  now  find  out  by  using  table  on 
page  58  how  many  circular  mils  there  are  in  a  No.  14 
wire — 4,107;  next  count  the  strands  in  the  wire  and 
say  we  count  7;  then,  by  multiplying  the  4,107  by  7 
we  will  find  the  circular  mils  in  the  whole  wire  or 
4,107  X  7  =  28,749  circular  mils  in  the  whole  wire. 
Now  find  the  nearest  corresponding  number  to  28,749 
in  circular  mil  table  and  we  find  it  is  26,250,  and 
looking  over  to  the  first  column  we  find  this  to  be  a 
No.  6  wire. 


58 


MOTION      PICTURE      PROJECTION 


CARRYING   CAPACITY  OF  COPPER  WIRK 


B.  &  S.  Gauge 

Circular  Mils 

Table  A 
Rubber  Insulation 
Ampere 

Table  B 
Other  Insulations 
Ampere 

18 

.',621 

3 

5 

16 

2,583 

6 

8 

14 

4,107 

15 

16 

12 

6,530 

17 

23 

10 

10,380 

24 

32 

8 

16,510 

35 

46 

6 

26,250 

50 

65 

5 

33,100 

54 

77 

4 

41,740 

65 

92 

3 

52,630 

76 

110 

2 

66,370 

90 

131 

1 

83,690 

107 

156 

0 

105,500 

127 

185 

00 

133,100 

150 

200 

000 

167,800 

177 

262 

0000 

211,600 

210 

312 

200,000 

200 

300 

300,000 

270 

400 

400,000 

330 

500 

500,000 

390 

590 

600,000 

450 

680 

700,000 

500 

760 

800,000 

550 

840 

900,000 

600 

920 

,000,000 

650 

,000 

,100,000 

690 

.070 

,200,000 

730 

,150 

,300,000 

770 

,220 

,400,000 

810 

,290 

,500,000 

850 

,360 

,600,000 

890 

,430 

1,700,000 

930 

,490 

1,800,000 

970 

,550 

1,900,000 

1,010 

,610 

?,000,000 

1,050 

.670 

The  lower  limit  is  specified  for  rubber-covered  wires  to  prevent  gradual 
deterioration  of  the  high  insulations  by  the  heat  of  the  wires,  but  not  from  fear 
of  igniting  the  insulation.  The  question  of  drop  is  not  taken  into  consideration 
in  the  above  tables. 


MOTION      PICTURE      PROJECTION  59 


MOTOR  GENERATORS 

A  motor  generator  is  simply  a  generator  or  set  of 
generators  connected  to  a  motor.  For  motion  picture 
work  the  generator  is  always  D.  C.  and  the  motor 
either  A.  C.  or  D.  C.  according  to  the  system  it  is  to 
be  used  on. 

Motor  generators  are  known  under  many  trade  names 
such  as  converters,  trans verters,  D.  C.  economizers. 

The  Hallberg  motor  generator  is  so  designed  and 
constructed,  that  it  may  be  connected  to  operate 
singly,  or,  if  two  are  installed  they  may  be  operated 
in  multiple,  thus  delivering  any  desired  amperage  from 
the  lowest  to  the  full  capacity  of  both  generators  to 
either  arc. 

The  Hallberg  twin  unit  system  gives  one  separate 
generator  for  each  arc,  when  dissolving  the  picture 
from  one  machine  into  the  other,  then  without  the 


Hallberg  Motor  Generator 
60  cycles  A.  C.  to  D.  C. 


60 


MOTION      PICTURE      PROJECTION 


Twin  Unit  System 
Arcs  in  multiple 

least  interference  the  current  at  the  projecting  arc  may 
be  doubled  for  perfect  screen  results  with  dark  films 
or  for  long  throws.  No  extra  emergency  transformer 
or  rheostat  is  required  with  the  twin  unit  system  as 
either  generator  may  be  used  on  either  projecting  arc 
at  a  moment's  notice. 


Double  Arc  Outfit 
Generator  wiring  for  double  arc 


MOTION      PICTURE      PROJECTION 


61 


The  arcs  (if  more  than  one)  with  a  Hallberg  generator 
are  always  connected  in  multiple.  This  is  of  great  ad- 
vantage because  it  is  thus  possible  to  deliver  the  maxi- 
mum ampere  output  of  the  generators  to  either  one 
of  the  arcs  for  very  dark  films.  This  would  not  be 
possible  with  generators  wound  for  arcs  in  series. 


Single  Arc  Outfit 

Generator  wiring  for  one  arc,  or  for  two  arcs, 
when  stealing  the  arcs 


62  MOTION      PICTURE      PROJECTION 


OPERATING  BOOTH 

The  booth  should  contain  everything  necessary  for 
perfect  projection,  but  nothing  that  can  be  done 
without.  Nothing  but  the  projection  of  films  should 
be  done  in  the  booth,  an  ante-room  should  be  provided 
with  work  bench  and  rewinder.  The  booth  should  be 
large  enough  to  permit  the  free  movements  of  the 
operator  or  operators  and  should  contain  the  necessary 
closets  and  shelves  for  the  operators'  clothes,  tools, 
supplies,  etc. 

The  operator  should  see  that  he  has  sufficient  sup- 
plies, such  as  fuses,  lugs,  film  cement,  asbestos  cable, 
condensers,  various  lubricants,  carbons,  mica,  brushes 
for  motor,  belting  and  a  few  of  the  necessary  parts  for 
machine  to  replace  those  parts  that  are  liable  to  need 
replacing  owing  to  wear,  etc. 

The  operator  should  carry  a  kit  of  tools  that  will 
permit  him  to  do  any  repair  work  that  he  may  be  called 
upon  to  do,  the  manager  of  today  has  very  little  use 
for  the  would-be  operator  who  shows  up  on  the  job 
with  a  ten  cent  pair  of  pliers  and  a  piece  of  string. 

If  using  rheostats  then  same  should  be  installed 
outside  the  booth,  as  should  mercury  arc  rectifiers. 
The  operator  will  thus  find  working  conditions  a  whole 
lot  more  comfortable. 

All  openings  such  as  projection  holes  and  port  holes 
should  be  so  equipped  with  shutters  that  they  will  all 
close  automatically  in  case  of  fire. 


MOTION      PICTURE      PROJECTION 


63 


A  lot  could  be  said  about  the  position  of  booth  and 
the  construction  of  same,  but  the  trouble  is  that  the 
operator  is  generally  the  last  man  a  manager  or  ex- 
hibitor will  consult  in  this  matter  when  planning  the 
theatre,  so  the  operator  has  to  work  under  conditions 
as  he  finds  them. 

One  thing  we  would  advise  and  that  is,  that  the  walls 
of  the  booth  should  be  painted  black  (if  same  has  not 
been  done) .  The  size  of  all  openings  should  be  reduced 
as  much  as  possible,  shade  all  lights  so  that  none  of  the 
light  finds  its  way  into  the  auditorium  of  theatre. 


Showing  the  take-up  mechanism 
of  Powers  machine 


64  MOTION     PICTURE     PROJECTION 


FILM 

The  film  used  for  motion  picture  work  is  similar  to 
that  used  in  ordinary  photographic  work,  only  it  gen- 
erally comes  to  the  operator  in  lengths  of  approximately 
1,000  feet.  The  size  of  each  picture  on  the  film  is  11-16 
by  15-16.  The  margin  of  the  film  is  perforated  (four 
holes  to  the  picture).  These  holes  engage  on  the  teeth 
of  the  sprockets. 

Never  lose  sight  of  the  fact  that  the  film  is  highly 
inflammable  and  should  at  all  times  be  kept  in  fire- 
proof boxes.  Great  care  should  be  taken  when  thread- 
ing the  machine  with  the  film,  to  see  that  it  does  not 
come  in  contact  with  the  hot  lamp  house.  All  film 
should  be  examined  before  showing.  While  this  is  no 
part  of  an  operator's  duties,  it  will  work  to  his  ad- 
vantage in  the  long  run. 

Under  no  conditions  let  your  film  run  on  to  the  floor 
of  the  booth.  Should  the  take-up  refuse  to  act  or  should 
the  film  break,  stop  the  machine  and  fix  it. 

There  are  a  number  of  ways  of  cleaning  film,  a 
number  of  machines  being  on  the  market  for  this  pur- 
pose, but  we  hold  that  the  cleaning  of  film  should  be 
done  in  the  film  exchange  and  not  by  the  operator;  an 
operator  is  paid  for  projecting  the  pictures  and  should 
be  able  to  give  his  undivided  attention  to  this. 

Operators  when  using  first  run  film  will  find  that  the 
emulsion  will  come  off  film  and  adhere  to  the  tension 
bars  and  film  runners  in  gate  of  machine.  A  very,  very 


MOTION      PICTURE      PROJECTION        65 

little  paraffin  or  vaseline  on  tension  bars  will  help  to 
overcome  this.  After  running  a  new  film  be  sure  to 
scrape  off  any  emulsion  that  may  be  on  the  machine, 
using  a  piece  of  soft  metal,  a  copper  penny  will  be 
found  suitable  for  this  purpose.  Failure  to  do  this  may 
mean  the  breaking  of  the  next  film  you  put  through 
the  machine  as  this  emulsion  will  cause  unnecessary 
tension. 

Film  Cement.  Should  you  run  out  of  cement  at  any 
time  you  can  tide  yourself  over  with  a  bottle  of  "New 
Skin,"  or  you  can  make  your  own  cement  as  follows: 

Equal  parts  of  .amyl  acetate  and  acetone,  or 

1  oz.  collodion  (New  Skin) 
1  oz.  banana  oil 
^2  oz.  ether,  or 

8  ozs.  of  acetone,  1  oz.  ether,  into  which  dissolve  a 
few  inches  of  film. 


66  MOTION      PICTURE      PROJECTION 


WIRING 

Conduit  system  must  be  installed  first,  with  con- 
ductors; metal  ends  must  be  bushed,  and  the  metal 
of  the  conduit  must  be  permanently  grounded.  For 
alternating  current  systems,  you  must  have  the  two  or 
more  wires  drawn  through  the  same  conduit.  It  is 
advised  that  this  be  done  on  direct  current  systems 
also,  in  case  same  is  ever  turned  into  an  A.  C.  system. 
The  same  conduit  must  never  contain  circuits  of  dif- 
ferent systems  but  may  contain  two  or  more  of  circuits 
of  the  same  system. 

Rubber-covered  wires  should  have  in  addition  to  the 
rubber  covering  placed  next  to  the  conductor  itself,  an 
outer  protective  covering  of  cotton  braid. 

The  neutral  wire  on  a  three  wire  system  may  be 
grounded  and  when  grounded  the  following  rules  must 
be  complied  with:  Must  be  grounded  at  the  central 
station  on  a  metal  plate  buried  in  coke  beneath  per- 
manent moisture  level  and  also  through  all  available 
underground  water  systems.  In  overhead  systems  the 
neutral  wire  must  be  grounded  every  500  feet. 


Flexible  armored  cable.    Twin  conductors 


MOTION      PICTURE      PROJECTION  67 


TESTING  FOR  GROUNDS 

Always  remember  that  like  poles  repel  each  other 
while  unlike  poles  attract  each  other,  in  other  words 
the  negative  polarity  is  attracted  by  the  positive 
polarity,  and  vice  versa,  while  the  negative  has  no 
attraction  for  negative  nor  the  positive  for  positive. 

The  positive  wire  of  one  system  will  have  no  attrac- 
tion for  the  negative  wire  of  any  other  system  except 
its  own,  nor  will  the  negative  of  one  system  find  any 
attraction  in  the  positive  of  any  other  system. 

A  ground  is  merely  the  current  from  one  polarity 
being  attracted  by  the  opposite  polarity,  through  the 
ground  or  some  conducting  medium  other  than  that 
in  the  circuit. 

In  a  three  wire  system  the  neutral  wire  is  always 
grounded. 

Now  supposing  that  we  are  working  on  a  three  wire 
system  and  our  neutral  wire  is  grounded,  and  that  we 
take  and  connect  one  of  the  outside  wires  to  the  upper 
jaw  of  arc  lamp,  and  we  connect  the  neutral  wire  to 
the  lower  jaw  (the  neutral  wire  now  acts  as  negative 
to  the  upper  or  positive  wire).  We  now  ground  the 
machine  by  connecting  the  metal  framework  of  machine 
to  the  conduit  coming  in  booth.  Our  machine  now 
becomes  grounded  on  the  neutral  because  we  have  made 
contact  between  the  frame  of  machine  and  the  already 
grounded  conduit.  Should  we  now  connect  our  test 
lamp  between  the  upper  jaw  of  arc  lamp  and  frame  of 


68  MOTION      PICTURE      PROJECTION 


Arc  lamp  with  carbons  fixed  in  position 
showing  the  various  adjustments 


MOTION     PICTURE     PROJECTION 69 

machine  or  lamp  house  we  will  naturally  get  a  light 
as  we  are  connected  between  the  two  polarities  of  the 
system. 

Now  should  the  arc  lamp  become  grounded  (caused 
we  will  say  by  the  mica  insulation  coming  out  of  jaw 
connection)  on  the  lower  jaw  it  would  mean  that  the 
system  is  grounded  on  the  negative  polarity  and  the 
arc  itself  is  grounded  on  the  negative  polarity,  and  this 
may  or  may  not  blow  the  fuse.  But  should  it  be  the 
upper  jaw  of  lamp  that  becomes  grounded  then  our 
arc  would  be  grounded  on  the  opposite  polarity  to  that 
of  the  machine,  and  thus  cause  a  short  circuit. 

To  test  for  a  ground  in  the  lamp  house,  first  dis- 
connect the  ground  wire  and  connect  the  terminals  of 
test  lamp  between  the  upper  and  lower  carbons.  We 
should  now  get  a  light  as  we  are  connected  between 
both  polarities,  this  test  merely  shows  that  we  have 
current  in  our  lamp. 

Now  connect  the  test  lamp  between  the  upper 
carbon  and  the  frame  of  lamp  house,  if  we  get  a  light 
then  our  lower  jaw  is  grounded,  if  we  do  not  get  light 
then  take  it  for  granted  that  lower  is  free  from  grounds. 

Now  test  to  see  if  the  upper  is  grounded  by  connecting 
the  test  lamp  between  the  lower  jaw  of  arc  lamp  and 
the  frame  of  lamp  house,  if  we  get  a  light  then  upper 
jaw  is  grounded.  Always  find  the  cause  of  ground 
and  remove  same  at  earliest  opportunity. 

Before  using  the  test  lamp  see  that  lamp  is  alright 
and  that  it  is  tight  in  socket. 

To  test  for  a  ground  in  the  rheostat,  use  a  bell  set. 
First  connect  the  terminals  of  bell  set  between  the  two 
binding  posts  of  rheostat,  and  if  rheostat  is  free  from 


70  MOTION      PICTURE      PROJECTION 

open  circuits  you  should  get  a  ring,  next  connect  the 
terminals  of  bell  set  between  one  of  the  coils  or  plates 
in  rheostat  and  the  iron  frame,  if  you  get  a  ring  it 
signifies  that  the  rheostat  is  grounded  but  this  test 
will  not  tell  you  which  coil  or  plate  is  causing  the 
ground.  To  find  exactly  where  ground  is,  proceed  as  fol- 
lows :  connect  bell  set  between  the  first  coil  and  frame, 
if  you  get  a  ring,  disconnect  the  first  coil,  now  connect 
between  the  second  coil  and  frame,  if  you  get  a  ring 
disconnect  the  second  coil,  and  do  the  same  to  third 
and  fourth  coil,  keep  testing  in  this  manner  till  bell 
stops  ringing,  then  the  coil  you  removed  last  was  the 
coil  that  was  grounded,  so  if  you  have  removed  six 
coils  and  the  bell  stops  ringing  when  connected  between 
the  seventh  coil  and  frame,  it  was  coil  number  six  that 
was  grounded. 

If  the  rheostat  is  made  of  more  than  one  section,  test 
each  section  separately  and  find  which  section  the 
ground  is  in,  then  proceed  as  above.  This  is  to  save 
time. 


MOTION      PICTURE      PROJECTION 


71 


FUSES 

A  safety  device  used  on  your  line  to  protect  the 
circuit. 

A  short  length  of  fusable  wire  introduced  in  a  circuit 
so  that  if  the  temperature  of  circuit  should  rise  above 
the  rated  capacity  of  fuse  the  wire  will  melt  and  thereby 
open  the  circuit. 

Fuses  are  made  in  different  shapes  and  sizes,  the 
moving  picture  operator,  however,  will  only  be  called 
upon  to  handle  the  under-mentioned. 


Copper-tipped  fuse  link 

Link  Fuse.  The  link  fuse  is  the  fuse  always  used  in 
the  booth,  being  of  the  open  type  it  cannot  be  readily 
boosted  without  same  being  plainly  seen.  Link  fuses 


Enclosed  or  "cartridge"  fuse 


Section  of  enclosed  fuse 


72 


MOTION      PICTURE      PROJECTION 


Powers  Cameragraph  No.  6A 
Showing  rheostat  and  motor  connections 


MOTION     PICTURE     PROJECTION  73 

have  no  protective  covering  so  should  always  be  in- 
stalled in  a  metal  cabinet. 

Cartridge  Fuse.  Made  by  connecting  two  metal  cap 
terminals  with  a  short  paper  tubing.  The  two  metal 
caps  are  connected  by  a  thin  wire  which  runs  through 
the  paper  tubing,  the  tubing  is  filled  with  some  non- 
conducting powder. 

Plug  Fuses.  Plug  fuses  are  used  for  protecting  the 
house  wiring  and  circuits  carrying  small  amperage. 

In  fusing  upon  any  circuit  you  must  take  into  con- 
sideration the  size  of  the  wire  used  and  the  amount 
of  amperage  to  be  drawn.  The  fuse  should  be  under 
the  carrying  capacity  of  the  wire  with  a  sufficient 
margin  to  allow  the  required  number  of  amperes  to 
pass  over  without  overheating.  The  rating  of  all  fuses 
is  marked  on  them.  Never  use  a  fuse  not  marked. 


Edison  fuse-plug 


MOTION      PICTURE      PROJECTION 


75 


PRINCIPALS  OF  OPTICAL  PROJECTION 

The  process  is  almost  the  reverse  of  ordinary  photog- 
raphy. For  instance  in  photography  a  scene  by  means 
of  the  photographic  objective  or  lens  is  photographed 
and  a  reduced  image  is  obtained  on  ground  glass.  This 
glass  is  replaced  by  a  sensitized  plate  and  by  the  use  of 
chemicals  the  image  is  fixed  thereon. 

In  projection  the  process  is  reversed,  that  is,  a  trans- 
parent slide  is  made  from  the  picture,  or  the  roll  of  film 
taken  with  the  motion  picture  camera  is  developed  and 
used  in  the  motion  picture  machine  (the  projector). 
By  means  of  a  condensed  light  they  are  strongly  illumi- 
nated and  with  an  objective  lens  an  enlarged  image  is 
projected  upon  the  screen,  this  screen  image  corres- 
ponding to  the  real  objects  photographed.  The  prin- 
ciples of  optical  projection  for  motion  picture  machine 
will  readily  be  understood  from  the  diagram  below. 


Showing  the  optical  system  of  a  moving  picture  circuit  and  how 
rays  of  light  travel  from  arc  E  to  screen  S 


76  MOTION     PICTURE     PROJECTION 

At  E  is  an  electric  arc  or  other  suitable  illuminant, 
the  light  from  which  is  caught  up  by  the  condenser  C. 
This  condenser  is  an  arrangement  of  lenses  so  con- 
structed as  to  gather  up  the  greatest  volume  of  light 
possible  and  to  concentrate  the  light  which  it  gathers 
at  the  center  or  diaphragm  plane  of 
the  objective  when  the  objective  is 
located  at  the  proper  distance  from 
the  film,  which  distance  is  deter- 
mined by  the  focal  length  of  ob- 
jective lens. 

The  film  should  be  placed  at  such 
a  point  that  the  entire  area  of  the 
aperture  in  gate  is  fully  illuminated, 
and  it  should  also  be  placed  so  that 
the  greatest  number  of  light  rays 
possible  should  pass  through  it. 

Proceeding  from  the  slide  D  or 
film  F  the  light  passes  through  the 
objective  0  where  the  rays  cross  and  the  object  is 
therefor  reversed,  by  means  of  the  objective,  the  object 
is  also  imaged  or  delineated  upon  the  screen  S,  the 
degree  of  sharpness  or  flatness  of  the  image  depends 
upon  the  optical  connection  of  the  lens. 

Great  care  should  be  taken  to  line  up  properly  the 
arc,  condensers  and  the  objective  lens,  as  under  the. 
best  of  conditions  less  than  5%  of  the  light  from  arc 
reaches  the  screen. 


MOTION      PICTURE      PROJECTION  77 


LENSES 

The  optical  system  of  a  moving  picture  circuit  com- 
prises : 

(a)  The  arc  lamp  or  mazda  lamp. 

(6)  The  condensers. 

(c)  The  lens,  or  objective. 

The  optical  system  is  a  very  important  one  and  one 
that  has  long  been  neglected  by  the  majority  of  oper- 
ators. A  number  of  men  who  have  been  operating 
machines  for  years  have  never  taken  the  lenses  apart 
and  have  no  idea  of  the  different  combinations  making 
up  the  objective  lens. 

There  is  no  motion  picture  book  published  that  we 
know  of  which  goes  far  enough  into  this  matter,  and 
we  would  advise  anyone  desirous  of  getting  all  the 
information  possible  on  lenses  to  study  the  books  dealing 
with  this  subject  that  may  be  found  in  the  various 
libraries. 

A  list  of  suitable  books  may  be  obtained  by  writing 
the  Technical  Editor  of  the  Motion  Picture  News,  New 
York  City. 

The  following  is  an  outline  of  what  an  operator 
should  know,  and  has  been  gathered  from  several  books 
dealing  with  optical  systems  and  lenses. 

Reflection.  The  change  of  direction  experienced  by 
a  ray  of  light  when  it  strikes  a  surface  and  is  thrown 


78 MOTION      PICTURE      PROJECTION 

back  or  reflected.    Light  is  reflected  according  to  two 
laws: 

(a)  The  angle  of  reflection  is  equal  to  the  angle  of 
incidence. 

(b)  The  incident  and  the  reflected  rays  are  both 
in  the  same  plane  which  is  perpendicular  to 
the  reflecting  surface. 

Refraction.  The  change  of  direction  which  a  ray  of 
light  undergoes  upon  entering  obliquely  a  medium  of 
different  density  from  that  through  which  it  has  been 
passing.  In  this  case  the  following  laws  obtain: 

(a)  Light  is  refracted  whenever  it  passes  obliquely 
from  one  medium  to  another  of  different  optical 
density. 

(b)  The  index  of  refraction  for  a  given  substance 
is  a  constant  quantity  whatever  be  the  angle 
of  incidence. 

(c)  The  refracted  ray  lies  in  the  plane  of  the  inci- 
dent ray  and  the  normal. 

(d)  Light  rays  are  bent  toward  the  normal  when 
they  enter  a  more  refracted  medium  and  from 
the  normal  when  they  enter  a  less  refracted 
medium. 

A  lens  may  be  defined  as  a  piece  of  glass  or  other 
transparent  substance  with  one  or  both  sides  curved. 
Both  sides  may  be  curved,  or  one  curved  and  the 
other  flat. 

The  object  of  the  lens  is  to  change  the  direction  of 
rays  of  light  and  thus  magnify  objects  or  otherwise 
modify  vision. 


MOTION      PICTURE      PROJECTION  79 

Lenses  may  be  classed  as : 

Double  convex  Double  concave 

Piano  convex  Piano  concave 

Concavo  convex  Convexo  concave 

The  focus  of  a  lens  is  the  point  where  the  refracted 
rays  meet. 

Spherical  Aberration.  The  reflected  rays  of  concave 
spherical  mirrors  do  not  meet  exactly  the  same  point. 
This  is  called  spherical  aberration. 

Effect  of  Spherical  Aberration.  It  produces  a  lack  of 
sharpness  and  defination  of  an  image.  If  a  ground 
glass  screen  be  placed  exactly  in  the  focus  of  a  lens  the 
image  of  an  object  will  be  sharply  defined  in  the  center 
but  indistinct  at  the  edges,  and  if  sharp  at  the  edges 
it  will  be  indistinct  at  the  center.  To  avoid  this  a 
disc  with  a  hole  in  the  center  is  placed  concentric  with 
the  principal  axis  of  the  lens,  thus  only  the  center  part 
of  the  lens  is  used. 

Chromatic  Aberration.  When  white  light  is  passed 
through  a  spherical  lens,  both  refraction  and  dispersion 
(the  decomposition  of  white  light  into  several  kinds 
of  light)  occur.  This  causes  a  separation  of  the  white 
light  into  the  various  colors  and  causes  images  to  have 
colored  edges.  This  effect  which  is  most  observable  in 
condenser  lenses  is  due  to  the  unequal  refrangibility  of 
the  simple  colors. 

Achromatic  Lenses.  The  color  effect  caused  by  the 
chromatic  aberration  of  a  simple  lens  greatly  impairs 
its  usefulness.  This  may  be  overcome  by  combining 


80  MOTION     PICTURE     PROJECTION 

into  one  lens,  a  convex  lens  of  crown  glass  and  a  concave 
lens  of  flint  glass. 

Back  Focal  Length.  The  distance  from  the  back  of 
the  lens  to  the  film  in  the  gate  of  machine  while  the 
film  is  in  focus  on  the  screen.  (Written  B.  F.) 

Equivalent  Focus.  The  distance  from  a  point  half 
way  between  the  back  and  front  combination  of  lenses 
to  the  film  in  the  gate  while  picture  is  in  focus  on  screen. 

Can  be  obtained  by  measuring  the  distance  between 
the  front  and  back  combination  then  dividing  by 
two  and  adding  the  result  to  the  back  focal  length. 
(Written  E.  F.) 

Objective  Lens.  The  objective  lens  of  a  moving  pic- 
ture machine  generally  consists  of  four  lenses,  two  in 
the  front  combination  and  two  in  the  rear.  The  two 
lenses  in  the  front  are  cemented  together  with  Canada 
Balsam  and  called  the  compound  lens.  The  back  com- 
bination consists  of  two  lenses  separated  by  a  metal 
ring,  called  the  duplex  lens. 

The  convex  or  greatest  convex  side  of  a  lens  always' 
faces  the  screen. 

It  is  absolutely  necessary  to  keep  the  lenses  clean,  it 
will  be  impossible  to  get  good  definition  or  sharp  focus 
on  the  screen  if  the  objective  lens  is  not  scrupulously 
clean.  Never  place  the  fingers  on  the  glass  surface 
of  lens,  as  though  it  may  not  show  when  looking  through 
the  lens  it  will  undoubtedly  affect  the  definition  of 
picture  on  screen. 

Condenser  lenses  should  be  cleaned  every  day,  and 
the  objective  lens  once  or  twice  a  week.  It  will  not  be 


MOTION      PICTURE      PROJECTION 


81 


found  necessary  to  take  the  lens  apart  to  do  this,  as  it 
will  only  be  the  exposed  glass  surfaces  that  will  need 
attention.  Use  a  clean  soft  handkerchief  for  this  pur- 
pose. The  lens  can  be  taken  apart  every  three  or  four 
months  and  all  surfaces  thoroughly  cleaned,  great  care 
should  be  taken  when  taking  the  lens  apart  so  that  you 
get  the  lenses  back  in  the  same  position  and  order. 


Fig.l 


Pi  §.2         Fi'£.3  Fig.  4 


Successful  results  in  projection  depend  largely  upon 
the  correct  adjustment  of  the  lamp,  which  must  throw 
a  brilliantly  illuminated  clear  circle  on  the  screen. 
After  the  objective  is  focused  as  will  be  evidenced  by 
a  sharp,  clear  image  on  the  screen,  examine  the  illumi- 
nated circle.  If  the  light  be  centered  and  the  lamp 
correctly  adjusted,  the  circle  will  be  entirely  free  from 
coloration  or  shadows.  In  Figures  1  and  2  the  crater 
of  arc  needs  to  be  properly  adjusted  laterally,  it  being 
as  shown  too  far  to  the  right  or  left.  Figures  3  and  4 


82 


MOTION      PICTURE      PROJECTION 


show  the  crater  too  high  or  too  low.  In  Figures  5,  6 
and  7  the  crater  is  too  near  or  too  far  away  from  con- 
densers. Figure  8  shows  it  in  right  position,  the  screen 
being  free  from  all  shadows  or  ghosts. 

This  shows  the  various  lenses :  (a)  double  convex ; 
(6)  piano  convex;  (c)  concavo  convex;  (d)  double  con- 
cave; (e)  piano  concave;  (/)  convexo  concave. 

The  first  three  are  thicker  at  the  center  than  at  the 
border,  and  are  called  converging;  the  second  three 
which  are  thinner  at  the  center  are  called  diverging. 


B 


MOTION      PICTURE      PROJECTION 


83 


LENS  TABLE  OF  FILM  PROJECTION 

DISTANCE  FROM  FILM  TO  SCREEN 


Stero. 

M.P. 

.Z5 

20 

25 

30 

35 

40 

45 

8 

2 

5.04 

6.74 

8.44 

10.14 

11.84 

13.54 

15.24 

6.72 

8.99 

11.25 

13.52 

15.78 

18.05 

20.31 

9 

2*A 

4.48 

5.99 

7.50 

9.01 

10.52 

12.03 

13.54 

5.97 

7.98 

10.00 

12.01 

14.03 

16.04 

18.05 

10 

21A 

4.02 

5.38 

6.74 

8.10 

9.46 

10.82 

12.18 

5.36 

7.17 

8.99 

10.80 

12.61 

14.42 

16.24 

11 

2H 

3.65 

4.89 

6.12 

7.36 

8.59 

9.83 

11.06 

4.87 

6.52 

8.17 

9.18 

11.46 

13.11 

14.76 

12 

3 

3.34 

4.47 

5.61 

6.74 

7.87 

9.00 

10.14 

4.46 

5.97 

7.48 

8.99 

10.50 

12.01 

13.52 

13 

3M 

3.08 

4.13 

5.17 

6.22 

7.26 

8.31 

9.35 

4.11 

5.50 

6.90 

8.19 

9.69 

11.08 

12.48 

14 

VA 

2.86 

3.83 

4.80 

5.77 

6.74 

7.72 

8.69 

3.81 

5.10 

6.40 

7.69 

8.99 

10.28 

11.58 

15 

3M 

2.66 

3.57 

4.47 

5.38 

6.28 

7.19 

8.10 

3.55 

4.76 

5.97 

7.17 

8.38 

9.59 

10.80 

16 

4 

2.49 

3.34 

4.19 

5.04 

5.98 

6.74 

7.59 

3.32 

4.45 

5.59 

6.72 

7.85 

8.98 

10.12 

17 

4M 

2.34 

3.14 

3.94 

4.74 

5.54 

6.34 

7.14 

3.12 

4.19 

5.25 

6.32 

7.38 

8.45 

9.52 

18 

4^ 

2.21 

2.97 

3.72 

4.48 

5.23 

5.99 

6.74 

2.95 

3.96 

4.96 

5.97 

6.98 

7.98 

8.99 

19 

4M 

2.09 

2.81 

3.52 

4.24 

4.95 

5.67 

6.38 

2.79 

3.74 

4.70 

5.65 

6.61 

7.56 

8.51 

20 

5 

1.98 

2.66 

3  34 

4.02 

4.70 

5.38 

6.06 

2.64 

3.55 

4.45 

5.36 

6.27 

7.17 

8.08 

21 

5M 

1.89 

2.54 

3.18 

3.83 

4.48 

5.13 

5.77 

2.51 

3.37 

4.24 

5.10 

5.96 

6.83 

7.69 

22 

5j^ 

1.80 

2.42 

3.04 

3.65 

4.27 

4.89 

5.51 

2.40 

3.22 

4.05 

4.87 

5.70 

6.52 

7.34 

23 

5M 

1.72 

2.31 

2.90 

3.49 

4.08 

4.67 

5.27 

2.29 

3.08 

3.87 

4.65 

5.44 

6.23 

7.02 

24 

6 

1.64 

2.21 

2.77 

3.34 

3.91 

4.47 

5.04 

2.19 

2.95 

3.70 

4.46 

5.21 

5.97 

6.72 

25 

VA 

1.57 

2.11 

2.66 

3.20 

3.75 

4.29 

4.83 

2.10 

2.82 

3.55 

4.27 

5.00 

5.72 

6.45 

26 

WA 

1.51 

2.03 

2.56 

3.08 

3.60 

4.12 

4.65 

2.02 

2.72 

3.41 

4.11 

4.81 

5.51 

6.20 

27 

6M 

1.45 

1.95 

2.46 

2.96 

3.46 

3.97 

4.47 

1.94 

2.61 

3.28 

3.95 

4.63 

5.30 

5.97 

28 

7 

.40 

1.89 

2.37 

2.86 

3.34 

3.83 

4.31 

.87 

2.52 

3.16 

3.81 

4.46 

5.11 

5.75 

29 

IX 

.35 

1.82 

2.29 

2.76 

3.23 

3.69 

4.16 

.80 

2.42 

3.05 

3.67 

4.30 

4.92 

5.69 

30 

7H 

.30 

1.75 

2.21 

2.66 

3.11 

3.57 

4.02 

.74 

2.34 

2.95 

3.55 

4.16 

4.76 

5.37 

31 

7M 

.26 

1.70 

2.14 

2.58 

3.01 

3.45 

3.89 

.68 

2.26 

2.85 

3.43 

4.02 

4.60 

5.19 

32 

8 

.22 

1.64 

2.07 

2.49 

2.92 

3.34 

3.77 

.62 

2.19 

2.75 

3.32 

3.89 

4.45 

5.02 

33 

8M 

.18 

1.59 

2.00 

2.42 

2.83 

3.24 

3.65 

.57 

2.12 

2.67 

3.22 

3.77 

4.32 

4.87 

34 

8^ 

.14 

1.54 

1.94 

2.34 

2.74 

3.14 

3.54 

.52 

2.05 

2.59 

3.12 

3.65 

4.19 

4.72 

35 

8M 

.11 

1.50 

1.88 

2.27 

2.66 

3.05 

3.43 

.48 

2.00 

2.51 

3.03 

3.55 

4.06 

4.58 

84 


MOTION     PICTURE     PROJECTION 


LENS  TABLE  OF  FILM  PROJECTION—  Continued 

DISTANCE  FROM  FILM  TO  SCREEN 


Ftero. 

M.P. 

60 

56 

60 

64 

70 

76 

80 

8 

2 

16.93 

18.97 

20.33 

21.69 

23.73 

25.77 

27.13 

22.58 

25.30 

27.11 

28.92 

31.64 

34.46 

36.17 

9 

2X 

15.05 

16.87 

18.07 

19.28 

21.09 

22.91 

24.12 

20.07 

22.48 

24.10 

25.71 

28.12 

30.54 

32.15 

10 

2Yz 

13.54 

15.17 

16.26 

17.34 

18.98 

20.61 

21.70 

18.05 

20.22 

21.67 

23.12 

25.30 

27.47 

28.92 

11 

2H 

12.30 

13.78 

14.77 

15.76 

17.24 

18.73 

19.72 

16.40 

18.38 

19.70 

21.01 

22.99 

24.97 

26.29 

12 

3 

11.27 

12.63 

13.54 

14.44 

15.80 

17.16 

18.07 

15.03 

.16.85 

18.05 

19.26 

21.07 

22.89 

24.10 

13 

3K 

10.40 

11.65 

12.49 

13.33 

14.58 

15.84 

16.67 

13.87 

15.54 

16.66 

17.77 

19.45 

21.12 

22.23 

14 

VA 

9.66 

10.82 

11.60 

12.38 

13.54 

14.71 

15.48 

12.87 

14.43 

15.46 

16.50 

18.05 

19.60 

20.64 

15 

3% 

9.00 

10.09 

10.82 

11.54 

12.63 

13.72 

14.44 

12.00 

13.46 

14:42 

15.39 

16.84 

18.29 

19.26 

16 

4 

8.44 

9.46 

10.14 

10.82 

11.84 

12.86 

13.54 

11.25 

12.61 

13.52 

14.42 

15.78 

17.14 

18.05 

17 

4X 

7.94 

8.90 

9.54 

10.18 

11.14 

12.10 

12.74 

10.58 

11.86 

12.72 

13.57 

14.85 

16.13 

16.98 

18 

4^ 

7.50 

8.40 

9.01 

9.61 

10.52 

11.42 

12.03 

9.10 

11.21 

12.01 

12.82 

14.03 

15.23 

16.04 

19 

&A 

7.10 

7.96 

8.53 

9.10 

9.96 

10.82 

11.39 

9.47 

10.61 

11.  .38 

12.14 

13.28 

14.43 

15.19 

20 

5 

6.74 

7.55 

8.10 

8.64 

9.46 

10.27 

10.82 

8.98 

10.07 

10.80 

11.52 

12.62 

13.70 

14.42 

21 

5K 

6.42 

7.20 

7.72 

8.23 

9.01 

9.79 

10.30 

8.55 

9.59 

10.28 

10.97 

12.00 

13.04 

13.73 

22 

5M 

6.13 

6.87 

7.36 

7.86 

8.60 

9.34 

9.83 

8.17 

9.16 

9.82 

10.47 

11.46 

12.45 

13.11 

23 

5% 

5.86 

6.57 

7.04 

7.51 

8.22 

8.93 

9.40 

7.81 

8.75 

9.38 

10.01 

10.96 

11.90 

12.53 

24 

6 

5.60 

6.28 

6.74 

7.19 

7.87 

8.55 

9.00 

7.48 

8.38 

8.99 

9.59 

10.50 

11.40 

12.01 

25 

6^ 

5.38 

6.03 

6.46 

6.90 

7.55 

8.20 

8.64 

7.17 

8.04 

8.62 

9.20 

10.07 

10.94 

11.52 

26 

6^ 

5.17 

5.80 

6.22 

6.63 

7.26 

7.89 

8^31 

6.90 

7.74 

8.39 

8.85 

9.69 

10.53 

11.08 

27 

6M 

4.98 

5.58 

5.98 

6.38 

6.99 

7.59 

8.00 

6.64 

7.44 

7.98 

8.52 

9.32 

10.13 

10.67 

28 

7 

4.80 

5.38 

5.77 

6.16 

6.74 

7.32 

7.71 

6.40 

7.18 

7.70 

8.21 

8.99 

9.77 

10.28 

29 

7M 

4.63 

5.19 

5.57 

5.94 

6.51 

7.07 

7.44 

6.17 

6.92 

7.42 

7.92 

8.67 

9.43 

9.93 

30 

7H 

4.47 

5.02 

5.38 

5.74 

6.28 

6.83 

7.19 

5.97 

6.69 

7.18 

7.66 

8.39 

9.11 

9.59 

31 

7M 

4.33 

4.86 

5.21 

5.56 

6.08 

6.61 

6.96 

5.77 

6.48 

6.95 

7.42 

8.12 

8.82 

9.29 

32 

8 

4.19 

4.70 

5.04 

5.38 

5.89 

6.40 

6.74 

5.58 

6.26 

6.72 

7.17 

7.85 

8.53 

8.98 

33 

8M 

4.06 

4.56 

4.89 

5.22 

5.71 

6.21 

6.54 

5.41 

6.07 

6.51 

6.95 

7.61 

8.27 

8.71 

34 

8H 

3.94 

4.42 

4.74 

5.06 

5.54 

6.02 

6.34 

5.25 

6.89 

6.32 

6.74 

7.38 

8.02 

8.44 

35 

SM 

3.82 

4.29 

4.60 

4.91 

5.38 

5.84 

6.15 

5.10 

5.72 

6.13 

5.65 

7.17 

7.79 

8.20 

MOTION      PICTURE      PROJECTION 


LENS  TABLE  OF  FILM  PROJECTION—  Continued 

DISTANCE  FROM  FILM  TO  SCREEN 


Stero. 

M.P. 

54 

90 

96 

100 

104 

110 

116 

8 

2 

28.49 

30.53 

32.57 

33.93 

35.29 

37.33 

39.36 

37.99 

40.71 

43.42 

45.24 

47.05 

49.77 

52.49 

9 

2*A 

25.32 

27.14 

28.95 

30.16 

31.37 

23.18 

34.99. 

33.76 

36.18 

38.60 

40.21 

41.82 

44  .  24 

46.55 

10 

21A 

22.78 

24.42 

26.05 

27.  14 

28.22 

29.86 

31.49 

30.37 

32.55 

34.72 

36.17 

37.62 

39.80 

41.97 

11 

2% 

20.70 

22.19 

23.67 

24.66 

25.65 

27.13 

28.61 

27.61 

29.59 

31.56 

32.88 

34.20 

36.18 

38.15 

12 

3 

18.97 

20.33 

21.69 

22.60 

23.50 

24.86 

26.22 

25.30 

27.12 

28.93 

30.14 

31.35 

33.16 

34.97 

13 

3J4 

17.51 

18.77 

20.02 

20.86 

21.69 

22.95 

24.20 

23.35 

25.02 

26.70 

27.81 

28.93 

30.60 

32.27 

14 

3K 

16.26 

17.43 

18.59 

19.37 

20.14 

21.31 

22.47 

21.68 

23.23 

24.78 

25.82 

26.86 

28.41 

29.96 

15 

3M 

15.17 

16.25 

17.34 

18.07 

18.79 

19.88 

20.97 

20.22 

21.67 

23.12 

24.09 

25.06 

26.51 

27.96 

16 

4 

14.22 

15.24 

16.25 

16.93 

17.61 

18.63 

19.65 

18.95 

20.31 

21.67 

22.58 

23.48 

24.84 

26.20 

17 

4M 

13.38 

14.34 

15.30 

15.94 

16.57 

16.52 

18.48 

17.83 

19.11 

20.39 

21.25 

22.10 

23.38 

24.66 

18 

4^ 

12.63 

13.54 

14.44 

15.05 

15.65 

16.56 

17.47 

16.85 

18.05 

19.26 

20.07 

20.87 

22  .  08 

23.29 

19 

4M 

11.96 

12.82 

13.68 

14.25 

14.83 

15.86 

16.54 

15.96 

17.10 

18.24 

19.10 

19.77 

20.92 

22.06 

20 

5 

11.36 

12.28 

12.99 

13.54 

14.08 

14.89 

15.71 

15.15 

16.23 

17.32 

18.05 

18.77 

19.86 

20.95 

21 

5M 

10.82 

11.60 

12.38 

12.89 

13.41 

14.19 

14.96 

14.42 

15.46 

16.49 

17.18 

17.87 

18.91 

19.94 

22 

VA 

10.33 

11.07 

11.81 

12.31 

12.80 

13.54 

14.28 

13.77 

14,76 

15.73 

16.40 

17.07 

18.06 

19.04 

23 

5M 

9.88 

10.59 

11.29 

11.77 

12.24 

12.95 

13.66 

13.16 

14.11 

15.06 

15.69 

16.32 

17.26 

18.21 

24 

6 

9.46 

10.14 

10.82 

11.27 

11.72 

12.40 

13.08 

12.61 

13.52 

14.42 

15.03 

15.63 

16.54 

17.45 

25 

VA 

9.07 

9.73 

10.38 

10.81 

11.25 

11.90 

12.55 

2.10 

12.97 

13.84 

14.42 

15.00 

15.87 

16.74 

26 

61A 

8.72 

9.35 

9.98 

10.40 

10.82 

11.44 

12.07 

11.64 

12.48 

13.31 

13.87 

14.43 

15.27 

16.10 

27 

6M 

8.40 

9.00 

9.60 

10.01 

10.41 

11.02 

11.62 

11.20 

12.01 

12.81 

13.35 

13.89 

14.69 

15:50 

28 

7 

8.10 

8.68 

9.27 

9.65 

10.04 

10.62 

11.21 

10.80 

11.58 

12.36 

12.87 

13.39 

14.17 

14.94 

29 

.  7M 

7.82 

8.38 

8.94 

9.32 

9.69 

10.26 

10.82 

10.42 

11.17 

11.93 

12.43 

12.93 

13.68 

14.43 

30 

7^ 

7.55 

8.10 

8.64 

9.00 

9.37 

9.91 

10.45 

10.08 

10.80 

11.53 

12.01 

12.50 

13.22 

13.95 

31 

7M 

7.31 

7.84 

8.36 

8.71 

9.07 

9.59 

10.12 

9.76 

10.46 

11.16 

11.63 

12.10 

12.80 

13.50 

32 

8 

7.08 

7.59 

8.10 

8.44 

8.78 

9.29 

-9.80 

9.44 

10.12 

10.80 

11.25 

11.70 

12.38 

13.06 

33 

81A 

6.86 

7.36 

7.85 

8.18 

8.51 

9.01 

9.50 

9.15 

9.81 

10.47 

10.91 

11.35 

12.01 

12  66 

34 

8^ 

6.66 

7.14 

7.62 

7.94 

8.26 

8.74 

9.22 

8.88 

9.52 

10.16 

10.58 

11.01 

11.65 

12.29 

35 

8M 

6.46 

6.93 

7.40 

7.71 

8.02 

8.48 

8.95 

8.62 

9.24 

9.86 

10.27 

10.6 

11.31 

11.93 

MOTION      PICTURE      PROJECTION  87 


LIGHT 

That  light  travels  with  a  speed,  which  is  much 
greater  than  the  speed  of  sound  is  shown  by  the  fact 
that  the  flash  of  a  distant  gun  is  always  seen  long  before 
the  sound  of  the  report  is  heard  and  that  lightning 
always  precedes  thunder. 

For  most  purposes  it  is  sufficiently  accurate  to  take 
the  velocity  of  light  as  186,000  miles  per  second. 

Light  always  travels  out  from  a  source  in  straight 
lines. 

Up  till  the  year  1800,  the  Corpuscular  theory  of  light 
was  the  one  most  generally  accepted,  that  light  consists 
of  streams  of  very  minute  particles,  or  corpuscles  pro- 
jected with  the  enormous  velocity  of  186,000  miles  per 
second  from  all  luminous  bodies.  The  facts  of  straight 
line  propagation  and  reflection  are  exactly  as  we  should 
expect  them  to  be  if  this  were  the  nature  of  light. 

A  usual  hypothesis  which  was  first  completely  for- 
mulated by  the  great  Dutch  physicist — Huygens  (1629- 
1695),  regarded  light  like  sound,  as  a  form  of  wave 
motion.  This  hypothesis  met  at  the  first  with  two 
very  serious  difficulties;  in  the  first  place  light,  unlike 
sound,  not  only  travels  with  perfect  readiness  through 
the  best  vacuum  which  can  be  obtained  with  an  air 
pump,  but  it  travels  without  any  apparent  difficulty 
through  the  great  interstellar  spaces  which  are  prob- 
ably infinitely  better  vacua  than  can  be  obtained  by 
artificial  means.  If  therefore,  light  is  a  wave  motion, 


88  MOTION      PICTURE      PROJECTION 

it  must  be  a  wave  motion  of  some  medium  which  fills 
all  space  and  yet  which  does  not  hinder  the  motion  of 
the  stars  and  planets.  Huygens  assumed  such  a  medium 
to  exist,  and  called  it  ether. 

The  second  difficulty  in  the  way  of  the  wave  theory 
of  light,  was  that  it  seemed  to  fail  to  account  for  the 
fact  of  straight  line  propagation.  Sound  waves,  water 
waves  and  all  other  forms  of  waves  with  which  we  are 
familiar  bend  readily  around  corners,  while  light  ap- 
parently does  not.  It  was  this  difficulty  chiefly  which 
led  many  of  the  famous  philosophers,  including  the 
great  Sir  Isaac  Newton,  to  reject  the  wave  theory  and 
to  support  the  projected  particle  theory. 

Within  the  last  hundred  years,  however,  this  difficulty 
has  been  completely  removed  and  in  addition  other 
properties  of  light  have  been  discovered,  for  which  the 
wave  theory  offers  the  only  satisfactory  explanation. 
If  the  wave  theory  is  to  be  accepted,  we  must  conceive 
with  Huygens,  that  all  space  is  filled  with  a  medium, 
called  the  ether,  in  which  the  waves  can  travel.  This 
medium  cannot  be  like  any  of  the  ordinary  forms  of 
matter;  for  if  any  of  these  forms  existed  in  interplane- 
tary space,  the  planets  and  the  other  heavenly  bodies 
would  certainly  be  retarded  in  their  motion.  As  a 
matter  of  fact,  in  all  the  hundreds  of  years  during  which 
astronomers  have  been  making  accurate  observation  of 
the  motion  of  heavenly  bodies  no  such  retardation  has 
ever  been  observed.  The  medium  which  transmits 
light  waves,  must  therefore  have  a  density  which  is 
infinitely  smaller  even  in  comparison  with  that  of  our 
lightest  gases.  The  existence  of  such  a  medium  is  now 
universally  assumed  by  physicists. 


MOTION      PICTURE      PROJECTION  89 

Just  as  sound  waves  are  disturbances  set  up  in  the 
air  by  the  vibrations  of  bodies  of  ordinary  dimensions, 
so  light  waves  are  disturbances  set  up  in  the  ether 
probably  by  the  vibrations  of  the  minute  corpuscles  or 
electrons,  of  which  the  atoms  of  ordinary  matter  are 
supposed  to  be  built  up.  Since  these  corpuscles  are 
extremely  small  in  comparison  with  ordinary  bodies  it 
is  not  surprising  that  their  rates  of  vibration  are  enor- 
mously larger  than  the  vibration  rates  of  tuning  forks, 
or  other  bodies  which  send  out  sound  waves.  Just  how 
these  corpuscles  are  set  into  vibration  and  in  just  what 
manner  they  vibrate,  we  cannot  say  as  yet  with  cer- 
tainty, but  since  we  do  know  that  an  increase  in  the 
temperature  of  all  bodies  means  an  increase  in  the 
agitation  of  the  molecules  and  atoms  of  which  these 
bodies  are  composed.  It  is  not  surprising  that  the 
vibrations  which  communicate  light  waves  to  the  ether 
take  place  in  general  in  bodies  which  have  a  high  tem- 
perature and  that  the  hotter  the  body  becomes  the 
more  intense  becomes  the  light  waves  which  it  emits. 


OBJECTIVE     LENS. 


JDUPLEX 
LENS 


Position  of  lenses  in  objective  lens 


MOTION      PICTURE      PROJECTION  91 


THREADING  THE  SIMPLEX  PROJECTOR 

Plate  I  shows  the  method  of  threading  the  film 
through  the  fire  trap,  and  under  the  top  sprocket. 

Plate  II  shows  how  the  film  is  threaded  through  the 
gate  of  machine,  by  forming  the  upper  loop,  with  the 
second  finger  of  the  left  hand  and  gripping  the  film 
below  the  intermittent  sprocket  with  the  first  and  third 
fingers  of  the  right  hand  and  closing  the  gate  by  tripping 
the  gate  spring  with  the  second  finger. 

Plate  III  illustrates  the  method  of  forming  the  lower 
loop,  threading  the  film  over  the  lower  sprocket,  and 
closing  the  lower  idler  by  a  downward  pressure  with 
the  first  finger  of  the  right  hand.  The  film  is  then 
threaded  through  the  lower  fire  trap  and  fastened  to 
the  reel  in  lower  magazine. 

Plate  IV  shows  the  machine  completely  threaded. 

Be  sure  and  see  that  the  sprocket  teeth  engage  in 
the  holes  of  film. 

See  that  the  film  goes  in  upside  down  and  emulsion 
side  to  some  of  light. 

Don't  forget  to  leave  film  loops  between  upper 
sprocket  and  intermittent  sprocket  and  between  inter- 
mittent sprocket  and  lower  sprocket. 

See  that  the  film  is  caught  on  lower  reel  before 
starting  the  motor. 


MOTION     PICTURE     PROJECTION  93 


QUESTIONS  AND  ANSWERS 

Ques.    What  is  a  gramme? 

Ans.  Unit  of  weight,  the  weight  of  a  cubic  centi- 
meter of  water  at  a  temperature  of  4  degrees  centigrade. 

Ques.    What  is  a  centimeter? 

Ans.  The  unit  of  length,  one  thousandth  millionth 
part  of  a  quadrant  of  the  earth's  surface. 

Ques.    What  is  a  coulomb? 

Ans.  Unit  of  quantity — quantity  of  current  which, 
impelled  by  one  volt  would  pass  through  one  ohm  in 
one  second. 

Ques.    What  is  a  joule? 

Ans.  The  unit  of  work,  the  work  done  by  one  watt 
in  one  second. 

Ques.    What  is  a  circular  mil? 

Ans.  A  unit  of  area,  a  mil  is  one  thousandth  part 
of  an  inch,  and  a  circular  mil  is  the  area  of  a  circle 
whose  diameter  is  one  mil. 

Ques.    What  is  ohms  law. 

Ans.  The  current  in  amperes,  is  equal  to  the  electric 
motive  force  in  volts,  divided  by  the  resistance  in  ohms. 

EXAMPLE.  If  we  had  100  volts  and  4  ohms  resistance 
in  our  circuit  we  would  get  the  amperage,  (current),  by 
dividing  100  (volts)  by  4  (ohms)  which  would  equal 
25  amperes. 


94  MOTION      PICTURE      PROJECTION 

The  resistance  in  ohms,  is  equal  to  the  electric  motive 
force  in  volts,  divided  by  the  current  in  amperes. 

EXAMPLE.  If  we  had  100  volts  and  25  amperes  then 
by  dividing  100  (volts)  by  25  (amperes)  we  would  get 
4  (ohms). 

The  electric  motive  force  is  equal  to  the  current  in 
amperes  multiplied  by  the  resistance  in  ohms. 

EXAMPLE.  If  we  had  25  amperes  and  4  ohms  re- 
sistance and  we  multiplied  them  we  would  get  100 
(volts). 

Ques.  How  would  you  judge  what  size  fuse  you 
would  use  on  your  line? 

Ans.  Take  into  consideration  the  size  of  the  wire 
and  the  amperage  to  be  drawn,  the  fuse  must  be  the 
weakest  part  of  the  circuit. 

Ques.  What  is  meant  by  conductor?  What  is  gen- 
erally used  for  this  purpose? 

Ans.  Anything  that  allows  the  passage  of  electricity 
through  it.  Copper. 

Ques.    What  is  the  carrying  capacity  of  a  No.  6 
rubber  covered  wire? 
Ans.    50  amperes. 

Ques.    What  is  the  carrying  capacity  of  a  No.  6 
weatherproof  wire? 
Ans.    65  amperes. 

Ques.  Name  the  three  kinds  of  wire  used  in  moving 
picture  work. 


MOTION      PICTURE      PROJECTION  95 

Ans.  Rubber  covered  wire  for  mains,  asbestos  cov- 
ered wire  for  lamp  leads  used  between  the  table  switch 
and  the  arc  lamp  (wherever  heat  is  generated)  and 
stage  cable  used  for  one  night  stands. 

Ques.  State  if  rubber  covered  wire,  weather-proof 
wire  and  asbestos  wire  are  all  fire-proof? 

Ans.  No,  weather-proof  wire  is  moisture  proof  but 
not  fire-proof. 

Ques.    What  size  wire  would  you  use  for  your  mains 
for  moving  picture  work? 
Ans.    Size  6  or  larger. 

Ques.  What  size  wire  would  you  use  for  your  motor 
connections  and  what  size  fuse? 

Ans.    Size  14  wire  and  a  6  ampere  fuse. 

Ques.    What  is  the  carrying  capacity  of  a  14  wire? 

Ans.    15  amperes. 

Ques.  On  direct  current  which  wire  would  you 
connect  to  the  top  carbon? 

Ans.    The  positive. 

Ques.    On  which  line,  your  positive  or  negative  would 
you  connect  your  rheostat? 
Ans.    On  either  line  it  makes  no  difference. 

Ques.  On  which  line  would  you  connect  a  trans- 
former? 

Ans.  A  transformer  must  be  connected  to  both  lines 
of  a  circuit. 

Ques.    What  is  asbestos  covered  wire? 

Ans.  A  cable  containing  very  fine  strands  of  copper 
wires  all  twisted  together  and  the  whole  thing  covered 
with  asbestos. 


96  MOTION      PICTURE      PROJECTION 

Ques.    What  is  rubber  covered  wire? 

Ans.  A  cable  either  solid  or  stranded  covered  with  a 
rubber  covering  and  an  outer  protective  covering  of 
cotton  braid. 

Ques.    What  is  stage  cable? 

Ans.  A  cable  containing  twin  conductors  each  in- 
sulated from  the  other  and  wrapped  with  a  composition 
covering. 

Ques.  How  would  you  connect  a  lug  to  one  of  the 
lamp  leads? 

Ans.  After  scraping  off  the  asbestos  insulation  would 
insert  cable  into  hole  of  lug  and  would  tighten  up  with 
pliers. 

Ques.    What  is  a  short  circuit? 

Ans.  Two  wires  of  opposite  polarity  coming  in  con- 
tact with  each  other  without  any  controlling  device. 

Ques.    What  is  a  rheostat  and  how  is  it  constructed? 

Ans.  An  instrument  used  on.  your  line  to  produce 
resistance  and  bring  the  current  to  a  fixed  working 
standard. 

It  is  made  of  a  number  of  metal  coils  or  plates  (gen- 
erally iron  or  german  silver)  connected  in  series  and 
mounted  on  some  insulated  material,  the  whole  thing 
being  enclosed  in  a  metal  cabinet. 

Rheostats  are  made  both  adjustable  and  non- 
adjustable. 

Ques.    Can  you  use  rheostats  on  A.  C.  or  D.  C.? 

Ans.  Rheostats  can  be  used  on  both  A.  C.  and  D.  C. 
but  it  is  cheaper  to  use  an  economizer  or  a  transformer 
instead  of  a  rheostat  on  A.  C. 


MOTION     PICTURE     PROJECTION  97 

Ques.  How  many  rheostats  would  you  use  on  110 
volts? 

A ns.    One  110  volt  rheostat  in  series  on  your  line. 

Ques.  If  automatic  shutter  on  Powers  machine  re- 
fused to  raise  when  machine  started  what  would  you  do? 

Ans.  Put  a  little  oil  in  oil  hole  in  top  of  movement; 
if  it  still  refused  to  raise,  would  take  off  casing  and  see 
if  shoes  or  springs  were  caught  or  dirty. 

Qu-es.-  Suppose  the  automatic  shutter  raised  up  when 
machine  started  but  would  not  stay  up  what  would 
you  do? 

Ans.    Put  a  little  heavy  oil  in  movement. 

Ques.  Suppose  the  automatic  shutter  did  not  drop 
when  machine  stopped  how  would  you  fix  it? 

Ans.  Put  a  little  thin  oil  in  movement,  and  if  this 
failed  examine  shoes  and  springs. 

Ques.  What  controls  the  size  of  the  picture  on  the 
screen? 

Ans.  The  focal  length  of  the  lens  and  the  distance 
of  machine  from  screen. 

Ques.    What  would  cause  a  travel  ghost  on  screen? 

Ans.    The  flicker  shutter  not  being  adjusted  right. 

Ques.  What  would  happen  if  the  take-up  belt  re- 
fused to  drive  take-up  or  fell  off  while  the  machine  was 
running? 

Ans.  Film  would  bunch  up  around  lower  sprocket 
and  then  fall  on  floor. 

Ques.  Name  six  revolving  parts  on  the  head  of 
machine  leaving  out  the  sprockets  and  idlers? 

Ans.  Flicker  shutter,  balance  wheel,  intermittent 
movement,  centrifugal  movement,  take-up  and  gears. 


98  MOTION      PICTURE      PROJECTION 

Ques.  Name  the  fire  prevention  devices  on  the  head 
of  machine. 

Ans.  Upper  and  lower  magazines,  upper  and  lower 
fire  traps,  upper  and  lower  fire  shields,  automatic 
shutter,  cooling  plate. 

Ques.  In  threading  machine  how  would  you  put  in 
film? 

Ans.  Upside  down  and  the  emulsion  side  towards 
lamp  house. 

Ques.    What    comprises    the    optical    system    in    a 
moving  picture  circuit? 
Ans.    The  source  of  light,  condensers  and  lens. 

Ques.    Name  some  of  the  various  kinds  of  lenses. 
Ans.    Double  convex,  double  concave,  piano  convex, 
piano  concave,  concavo-convex. 

Ques.  What  is  meant  by  the  back  focal  length  of  a 
lens? 

Ans.  The  distance  from  the  back  of  the  lens  to  the 
film  in  gate  while  the  picture  is  in  focus  on  screen. 

Ques.    Of  what  use  are  the  condensers? 
Ans.    To  bring  the  light  of  arc  lamp  to  a  point  of 
focus  on  aperture  in  gate. 

Ques.    Which  end  of  the  lens  goes  towards  the  screen? 
Ans.    The  greatest  convex  side. 

Ques.    What  is  meant  by  a  keystone  effect? 

Ans.  When  the  machine  is  set  up  above  the  level  of 
the  screen  and  it  is  necessary  to  tilt  the  machine,  the 
bottom  of  the  picture  will  be  wider  than  the  top,  owing 


MOTION     PICTURE     PROJECTION  99 

to  the  light  rays  having  to  travel  further  to  the  bottom 
of  the  screen  than  to  the  top. 

Ques.    Give  your  definition  of  motion  pictures. 
Ans.    An  optical  illusion  based  on  the  persistence  of 
vision. 

Ques.    What  is  a  fuse,  and  how  many  kinds  are  there? 

Ans.  A  fuse  is  a  safety  device  used  on  your  line  .to 
protect  your  circuit.  Plug  fuses,  cartridge  fuses  and 
link  fuses. 

Ques.  How  many  sets  of  fuses  do  you  use  on  your 
line  for  motion  picture  work  and  what  would  you  call 
them? 

Ans.    Two,  main  and  booth  fuses. 

Ques.  What  size  fuse  would  you  use  at  the  main  and 
what  size  at  booth,  using  No.  6  wire? 

Ans.  Fifty  ampere  cartridge  fuse  at  main  and  45 
ampere  link  fuse  in  booth. 

Ques.  Why  not  use  a  45  ampere  cartridge  fuse  in 
booth? 

Ans.  The  department  calls  for  the  use  of  link  fuses 
only;  the  reason  cartridge  fuses  cannot  be  used  in 
booth  is  that  cartridge  fuses  are  easily  tampered  with 
or  boosted. 

Ques.  Why  do  you  use  a  smaller  size  fuse  in  the 
booth  than  you  do  on  your  mains? 

Ans.  So  that  in  case  of  trouble  the  fuse  in  the  booth 
will  go  first  (it  being  the  weakest  part  of  the  circuit) 
and  you  will  not  have  to  run  down  to  main  fuses  in 
cellar  as  you  would  have  to  do  if  main  fuses  were  to 
blow. 


100  MOTION      PICTURE      PROJECTION 

Ques.    How  would  you  install  a  link  fuse? 
Ans.    On  a  slate  base  in  a  metal  cabinet  fitted  with 
a  self-closing  door. 

Ques.  What  would  happen  on  your  line  if  you  got  a 
short  circuit? 

Ans.    Blow  your  fuses. 

Ques.  Can  you  use  a  60  ampere  cartridge  fuse  on 
your  mains  on  a  No.  6  wire? 

Ans.  No,  as  this  would  be  overfusing,  the  carrying 
capacity  of  a  No.  6  wire  is  50  amperes,  and  the  fuses 
must  be  the  weakest  part  of  your  circuit. 

Ques.    What  is  an  ampere,  a  volt  and  an  ohm? 

Ans.  The  ampere  is  the  unit  of  current,  the  volt  is 
the  unit  of  electric  motive  force  (or  pressure),  and  the 
ohm  is  the  unit  of  electrical  resistance. 

Ques.    What  is  a  watt? 

Ans.  The  electrical  unit  of  power.  Amperes  times 
volts  equals  watts. 

Ques.    What  is  a  kilowatt? 

Ans.    1,000  watts  equals  one  kilowatt. 

Ques.    How  many  w'atts  in  one  horse  power? 
Ans.    746  watts  equal  one  horse  power. 

Ques.    What  is  an  ampere-hour? 

Ans.   Current  in  amperes  multiplied  by  time  in  hours. 

Ques.    What  is  a  second? 

Ans.  The  unit  of  time,  the  time  of  one  swing  of  a 
pendulum  making  86,400  swings  in  a  solar  day. 


MOTION      PICTURE      PROJECTION          ' J>  1J0'J 

Ques.  What  is  meant  by  the  safe  carrying  capacity 
of  wires? 

Ans.  All  wires  will  heat  when  a  current  of  electricity 
passes  through  them.  The  greater  the  current  or  the 
smaller  the  wire,  the  greater  will  be  the  heating  effect. 
Large  wires  are  heated  comparatively  more  than  small 
wires  because  the  latter  have  a  relatively  greater  radi- 
ating surface. 

Ques.  What  parts  of  a  dynamo  are  liable  to  be  short 
circuited? 

Ans.  The  terminals,  brush  holders,  commutator, 
armature  coils  and  field  coils. 

Ques.  Suppose  on  looking  over  your  motor  you 
found  that  there  were  several  ridges  on  the  commutator, 
where  would  you  look  for  the  cause? 

Ans.  The  brushes  are  not  set  right  or  the  tension  of 
brushes  on  commutator  is  too  great. 

Ques.  How  would  you  go  about  setting  a  Simplex 
flicker  shutter? 

Ans.  When  setting  the  shutter,  set  the  framing  lever 
in  center,  move  the  shutter  adjusting  block  to  a  point 
equidistant  between  the  two  pins  by  means  of  the  knob 
on  the  back  of  the  mechanism  facing  towards  lamp 
house.  Four  teeth  on  intermittent  sprocket  represents 
one  full  move  of  one  section  on  star,  moving  the  sprocket 
two  teeth  either  backward  or  forward  would  mean 
center.  Now  adjust  shutter  as  follows:  On  a  three 
wing  shutter  the  center  of  the  blade  with  the  word 
"Simplex"  stamped  on  it  should  be  on  center  with  the 
lens;  on  a  two  wing  shutter  the  center  of  either  blade 
will  cover  the  lens.  The  position  can  best  be  determined 


L02  MOTION      PICTURE     PROJECTION 

by  the  set  screw  on  the  spider,  which  should  face  the 
operator  in  a  horizontal  position.  In  setting  shutter 
always  keep  as  close  to  the  lens  as  possible. 

Ques.  What  is  a  D.  C.  to  D.  C.  motor  generator? 

Ans.  It  is  a  D.  C.  motor  connected  to  a  D.  C.  genera- 
tor, used  to  give  a  D.  C.  controlled  light  at  arc,  thereby 
doing  away  with  the  use  of  rheostats.  When  we  take 
into  consideration  the  fact  that  a  rheostat  on  110  volt 
circuit  wastes  from  35%  to  50%  of  the  current,  and 
on  220  volts,  rheostats  wastes  from  65%  to  75%  it  will 
be  easily  seen  why  a  D.  C.  generator  should  be  installed 
in  place  of  rheostats. 

Ques.  Show  by  figures  what  would  be  the  saving  if 
you  installed  a  Hallberg  D.  C.  generator  and  discarded 
your  rheostats,  taking  it  for  granted  that  you  were 
drawing  80  amperes  at  the  arc  on  a  110  volt  circuit? 

Ans.  With  rheostats  we  would  be  consuming  110 
volts  times  80  amperes  or  8,800  watts  while  with  the 
generator  we  would  be  consuming  1 10  volts  times  57  amp- 
eres (this  being  the  amount  of  current  generator  draws 
from  line)  or  6,270  watts.  With  rheostats  we  consume 
8,800  watts  per  hour  while  with  generator  we  only 
consume  6,270  watts  per  hour,  the  generator  showing 
a  saving  of  1,530  watts  per  hour. 

Ques.  State  what  advantage  a  motor  generator  has 
over  rheostats  aside  from  the  question  of  current  saving. 

Ans.  You  do  away  with  the  heat  generated  by  the 
rheostats. 

Ques.  What  is  a  Hallberg  4  in  1  automatic  regulator? 

Ans.  Consists  of  an  adjustable  transformer  with 
separate  line  and  lamp  coils.  The  primary  coil  is 


MOTION     PICTURE     PROJECTION  103 

wound  in  two  sections  each  section  insulated  from  the 
other.  Each  section  is  wound  for  110  volts.  For  110 
volts  you  connect  the  two  sections  in  multiple  while 
for  220  volts  you  connect  the  two  sections  in  series.  It 
is  used  for  moving  picture  circuits  when  using  the 
mazda  lamp  instead  of  arc.  (See  page  33.) 

Ques.  What  is  meant  by  stealing  the  arc? 

Ans.  When  two  arcs  are  connected  to  one  source  of 
supply,  as  when  two  arcs  are  connected  to  one  genera- 
tor, and  where  the  striking  of  the  second  arc  automati- 
cally puts  out  or  draws  from  the  first  arc. 

Ques.  What  is  meant  by  the  strength  of  a  current? 
Ans.    The  quantity  of  electricity  which  flows  past 
any  point  of  the  circuit  in  one  second. 

Ques.  What  is  the  difference  between  a  dynamo  and 
an  alternator? 

Ans.  A  dynamo  generates  D.  C.  while  an  alternator 
generates  A.  C. 

Ques.  Suppose  you  had  one  110  volt  25  ampere 
rheostat  connected  on  a  110  volt  circuit  D.  C.  and  you 
had  one  110  volt  25  ampere  rheostat  connected  on  a 
110  volt  circuit  A.  C.  at  which  arc  would  you  draw 
the  most  amperage  and  why? 

Ans.  On  the  A.  C.  arc  because  with  A.  C.  you  have 
to  feed  the  carbons  closer  together  than  on  D.  C.  and* 
that  draws  a  little  more  amperage. 

Ques.  How  does  a  dynamo  create  current? 

Ans.  It  does  not  create  current  but  generates  an 
induced  E.  M.  F.  which  causes  a  current  to  flow  through 
a  circuit. 


104  MOTION     PICTURE     PROJECTION 

Ques.  How  should  a  knife  switch  be  installed? 

Ans.    So  that  gravity  tends  to  open  same. 

Ques.  Is  it  possible  to  reverse  the  rotation  of  a  motor, 
if  so  how? 

Ans.  Yes,  by  reversing  the  current  through  the 
fields  or  the  current  through  the  armature. 

Ques.  What  is  the  difference  between  a  D.  C.  and  an 
A.  C.  rheostat? 

Ans.  Rheostats  are  made  for  either  A.  C.  or  D.  C. 
There  is  no  difference  between  them. 

Ques.  How  many  rheostats  would  you  use  on  220 
volts  and  how  would  you  connect  same? 

Ans.  One  220  volt  rheostat  in  series  with  your  line 
or  two  110  volt  rheostats  in  series  with  each  other  and 
in  series  on  your  line. 

Ques.  With  55  volts  coming  in,  how  many  rheostats 
would  you  use,  and  how  would  you  connect  same? 

Ans.  Use  two  110  volt  rheostats  in  multiple  with 
each  other  and  in  series  on  your  line. 

Ques.  What  effect  does  it  have  by  connecting  rheo- 
stats in  multiple  and  rheostats  in  series? 

Ans.  Rheostats  in  series  gives  you  the  sum  of  their 
resistance,  for  instance  if  they  each  offered  4  ohms 
resistance  and  we  connected  same  in  series  with  each 
other  we  would  have  8  ohms  resistance  on  our  line.  If 
we  connected  the  same  two  rheostats  in  multiple  we 
would  only  then  have  approximately  2  ohms  resistance. 

Ques.  Why  don't  they  use  copper  coils  instead  of 
iron  in  a  rheostat? 

Ans.  Because  iron  offers  more  resistance  than 
copper,  copper  being  a  good  conductor. 


MOTION      PICTURE      PROJECTION  105    - 

Ques.    Is  all  the  resistance  offered  in  your  rheostat? 

Ans.  No,  everything  on  your  line  offers  resistance, 
all  substance  offers  resistance  to  the  passage  of  elec- 
tricity through  them,  the  amount  of  resistance  de- 
pending on  the  substance  and  its  size,  that  is  on  its 
length  and  cross  section. 

Ques.  Do  metals  offer  more  or  less  resistance  when 
hot? 

Ans.  The  resistance  of  all  metals  increases  with  an 
Increase  of  temperature,  while  carbons  and  insulating 
materials  decrease  with  an  increase  of  temperature. 

•  Ques.    Is  it  possible  to  get  a  short  circuit  in  the 
rheostat  ? 

Ans.  Yes,  when  the  arc  lamp  is  burning,  as  you  then 
have  two  polarities  in  rheostat. 

Ques.  How  many  kinds  of  current  are  there  and 
state  what  they  are. 

Ans.    Two,  direct  current  and  alternating  current. 

Ques.    What  is  meant  by  direct  current? 

Ans.  Direct  current  is  a  current  that  always  flows 
in  the  same  direction;  always  leaves  the  dynamo 
through  the  positive  pole  and  returns  through  the 
negative  pole. 

Ques.    What  is  alternating  current? 

Ans.  Alternating  current  is  a  current  that  changes 
its  flow  of  direction  so  many  times  a  second.  Each 
part  of  the  circuit  being  so  many  times  positive  and  so 
many  times  negative  every  second. 


106  MOTION      PICTURE      PROJECTION 

Ques.    What  is  current  frequency? 

Ans.  The  number  of  times  alternating  current 
changes  its  flow  of  direction  in  a  second.  (These 
changes  are  called  cycles). 

Ques.  Which  current  is  the  best  for  moving  picture 
work  and  why? 

Ans.  Direct  current,  gives  a  better  arc,  more  easily 
controlled,  and  is  not  so  noisy  as  A.  C. 

Ques.    Is  it  possible  to  change  A.  C.  into  D.  C.? 

Ans.  Yes,  there  are  various  machines  on  the  market 
for  this  purpose — transverters,  arc  rectifiers  and  motor 
generator  sets. 

Ques.  Suppose  you  had  110  volts  D.  C.  coming  into 
the  theatre  and  you  had  one  110  volt  rheostat  on  your 
line,  and  then  the  current  was  changed  from  D.  C.  to 
A.  C.  what  changes  would  you  make  on  your  line  and 
state  reasons  why. 

Ans.  Would  take  off  the  rheostat  and  install  an 
economizer  (step-down  transformer)  this  would  give  me 
a  saving  of  about  66%  (makers  claim) . 

Ques.  Suppose  you  changed  a  rheostat  for  an  econ- 
omizer on  a  220  volt  line,  would  there  be  a  saving? 
If  so,  about  how  much? 

Ans.    About  80%  (makers  claim). 

Ques.  State  an  easy  way  to  test  whether  you  have 
A.  C.  or  D.  C.  at  arc  lamp,  and  if  you  are  on  D.  C. 
whether  you  are  connected  right  (positive  line  con- 
nected to  top  carbon). 

Ans.  First  strike  the  arc  and  let  it  burn  a  second  or 
two,  then  throw  off  the  switch  and  open  lamp  house 


MOTION      PICTURE      PROJECTION  107 

door,  if  both  carbons  remain  red  for  the  same  length  of 
time  we  have  A.  C.  but  should  one  carbon  remain  red 
longer  than  the  other  we  have  D.  C.  The  top  carbon 
should  remain  red  longest,  so  if  the  bottom  remains  red 
longer  than  the  top  one  we  know  that  we  are  burning 
upside  down.  (Positive  line  is  connected  to  bottom 
carbon  instead  of  to  top.) 

Ques.    Suppose  you  find  you   are  burning  upside 
down,  where  on  your  line  would  you  make  the  change? 
Ans.    At  table  switch,  arc  lamp  or  wall  switch. 

Ques.  Could  you  change  polarity  at  the  rheostat  if 
you  were  burning  upside  down? 

Ans.  No,  as  you  have  only  one  polarity  at  the 
rheostat. 

Ques.  What  is  meant  by  constant  current  type  of  a 
current  rectifying  device? 

Ans.  Where  two  arc  lamps  are  connected  to  one 
apparatus  like  a  transverter  or  a  motor  generator, 
and  where  the  voltage  and  not  the  amperage  is  doubled 
when  both  arcs  are  struck.  For  instance  if  we  had  one 
arc  operating  at  55  volts  and  50  amperes  and  we  struck 
the  second  arc  we  should  then  have  two  arcs  operating 
at  50  amperes  110  volts  (approximately). 

Ques.    What  is  a  three  wire  system? 

Ans.  A  distribution  system  invented  by  Edison, 
where  two  dynamos  are  connected  in  series  and  the 
third  or  neutral  wire  is  taken  from  a  point  common  to 
both  dynamos. 

Ques.  How  many  rheostats  would  you  use  if  you 
were  using  the  two  outside  wires  of  a  three  wire  system? 


108  MOTION      PICTURE      PROJECTION 

Ans.  Two  110  volt  rheostats  in  series  with  each 
other,  as  between  the  outside  wires  we  would  have 
220  volts. 

Ques.  Suppose  you  were  drawing  50  amperes  off  one 
side  of  a  three  wire  system  and  40  amperes  off  the  other, 
how  many  amperes  would  be  flowing  in  the  neutral  wire? 

Ans.  As  the  amount  of  current  in  the  neutral  wire 
is  the  difference  between  the  amperage  drawn  off  either 
side,  we  would  have  a  flow  of  10  amperes  in  the  neutral 
wire. 

Ques.  Suppose  that  we  were  drawing  45  amperes  off 
either  side  of  a  three  wire  system  what  would  be  the 
amount  of  amperage  flowing  in  the  neutral  wire? 

Ans.  If  we  were  drawing  45  amperes  off  each  side  of 
the  system,  the  system  would  be  balanced  and  there 
would  be  no  flow  of  current  in  the  neutral  wire. 

Ques.  What  are  the  advantages  of  a  three  wire 
system? 

Ans.  The  saving  of  copper  is  the  advantage  of  the 
system,  as  by  its  use  the  size  of  the  conductors  may  be 
reduced,  by  increasing  the  pressure  at  which  the  cur- 
rent is  transmitted,  without  increasing  the  voltage  of 
the  lamps.  If  for  example  the  neutral  wire  is  made  the 
same  size  as  the  two  outside  wires,  the  total  weight  of 
the  copper  for  the  three  wire  system,  will  be  three- 
eighths  (3-8)  of  that  required  for  two,  two  wire  systems 
for  the  same  load,  distance  and  percentage  of  loss. 

Ques.  What  are  the  disadvantages  of  a  three  wire 
system? 

Ans.  The  system  is  more  complicated,  the  cost  of 
the  switches,  panel  boards,  etc.,  is  increased,  that  the 


MOTION      PICTURE      PROJECTION  109 

system  is  more  subject  to  disturbances,  if  for  example- 
the  fuse  on  the  neutral  wire  should  melt,  the  lamps  on 
the  system  might  be  considerably  damaged  in  case  the 
two  sides  of  the  system  were  not  balanced. 

Ques.  Can  you  connect  between  the  positive  and 
neutral  wire  for  moving  picture  work? 

Ans.    Yes,  you  will  then  need  one  1 10  volt  rheostat. 

Ques.   Which  wire  on  a  three  wire  system  is  grounded  ? 
Ans.    The  neutral  wire. 

Ques.  If  we  were  connected  on  the  positive  and 
neutral  wires  of  a  three  wire  system,  and  we  got  a 
ground  on  the  lower  jaw  of  arc  lamp,  would  that  blow 
the  fuse. 

Ans.  No,  all  metal  machines  must  be  grounded,  and 
by  so  doing  the  lamp  house  becomes  the  same  polarity 
as  the  neutral  wire.  Therefore  the  ground  being  on 
lower  jaw  which  is  neutral  and  the  same  polarity  as 
lamp  house,  it  may  not  blow  the  fuse. 

Ques.  What  is  a  transformer,  how  is'  it  made  and 
how  does  it  work? 

Ans.  A  transformer  consists  of  two  copper  coils,  the 
primary  and  the  secondary,  and  a  laminated  iron  core. 
The  two  coils  are  insulated  from  one  another  and  from 
the  core.  The  primary  coil  is  connected  to  the  source 
of  supply  and  the  secondary  is  connected  to  the  lamp. 
As  a  matter  of  fact  these  coils  are  each  usually  made  of 
several  sections.  The  voltage  induced  in  the  secondary 
coil  is  equal  to  the  voltage  impressed  on  the  primary 
coil  multiplied  by  the  ratio  of  the  number  of  turns  in 
the  secondary  to  the  number  in  the  primary  coil,  less  a 


110         _       MOTION      PICTURE      PROJECTION 

certain  drop  due  to  impedance  of  the  coils  and  to 
magnetic  leakage.  This  drop  is  negligible  on  no  load. 
Step-up  transformers  are  used  to  raise  the  voltage. 
Step -down  transformers  are  used  to  step  down  the 
voltage.  The  efficiencies  of  transformers  are  high, 
varying  from  94%  to  95%  at  one-fourth  load  to  98% 
at  full  load  for  sizes  above  25  K.  W. 

The  current  enters  the  transformer  through  the 
primary  coil  and  the  alternations  of  the  current  in  this 
coil  sets  up  a  magnetic  field  in  the  transformer.  The 
secondary  cuts  the  lines  of  magnetic  force  and  carries 
off  a  new  current  to  the  arc  lamp. 

Ques.  Does  a  transformer  change  the  current  from 
A.  C.  to  D.  C.? 

Ans.  No,  it  gives  off  a  magnetized  A.  C.  current  to 
arc  lamp. 

Ques.    Can  you  use  a  transformer  on  direct  current? 
Ans.    No. 

Ques.  Why  do  they  make  the  core  of  a  transformer 
of  a  soft  metal  like  iron,  instead  of  steel? 

Ans.  Because  the  softer  the  metal  the  more  easily  it 
is  to  magnetize  and  it  will  lose  its  magnetism  quicker 
after  the  current  has  been  shut  off. 

Ques.    State  in  one  word  how  an  economizer  or  trans- 
former works. 
Ans.    Induction. 

Ques.    What  is  meant  by  induction? 

Ans.  A  charged  body  running  parallel  to  another 
body  (it  being  a  conductor)  tends  to  charge  the  neigh- 
boring body  without  any  tangible  form  of  connection. 


MOTION      PICTURE      PROJECTION  111 

Ques.  How  are  the  coils  in  a  transformer  or  econo- 
mizer connected,  in  multiple  or  series? 

Ans.  They  are  not  connected,  they  are  insulated 
from  each  other. 

Ques.  What  is  the  difference  between  an  economizer, 
an  inductor  and  a  step-down  transformer? 

Ans.  None,  they  are  all  the  same  and  answer  the 
same  purpose. 

Ques.  Where  on  your  line  would  you  connect  your 
economizer  and  why? 

Ans.  Between  the  table  switch  and  the  arc  lamp,  so 
that  by  pulling  the  table  switch  you  put  the  arc  and 
the  economizer  out  of  commission  at  the  same  time, 
whereas  if  economizer  was  connected  between  the  table 
switch  and  the  wall  switch  it  would  be  necessary  to 
pull  both  switches  or  at  least  pull  wall  switch  to  put 
both  out  of  commission. 

Ques.    How  many   working   parts   are   there   in   a 
transformer? 
Ans.    None. 

Ques.  Where  is  the  difference  between  a  step-up 
and  a  step-down  transformer? 

Ans.    In  the  ratio  of  the  coil  windings. 

Ques.    What  is  a  transverter? 

Ans.  A  motor  generator  set,  an  A.  C.  motor  con- 
nected to  a  D.  C.  generator  gives  a  D.  C.  current  at 
arc  lamp.  Or  a  D.  C.  motor  connected  to  a  D.  C. 
generator  that  gives  a  controlled  D.  C.  current  at 
arc  lamp. 


112  MOTION      PICTURE      PROJECTION 

Ques.    What  is  a  mercury  arc  rectifier  used  for? 
Ans.    To  change  A.  C.  to  D.  C. 

Ques.  What  is  the  difference  between  a  motor,  a 
motor  generator  and  a  generator? 

Ans.  A  motor  transforms  electrical  into  mechanical 
power.  A  generator  transforms  mechanical  power  into 
electrical  power.  A  motor  generator  is  a  device  consis- 
ting of  a  motor  mechanically  connected  to  one  or  more 
generators. 

Ques.  What  is  the  difference  between  a  starting  box 
and  a  speed  regulator? 

Ans.  Motor  starting  rheostats  or  starting  boxes  are 
designed  to  start  a  motor  and  bring  it  gradually  from 
rest  to  full  speed.  They  are  not  intended  to  regulate 
speed  and  must  not  be  used  for  that  purpose.  Failure 
to  observe  this  caution  will  result  in  burning  out  the 
resistance  which  in  a  motor  starter  is  sufficient  to  carry 
the  current  for  a  limited  time  only,  whereas  in  a  speed 
regulator,  sufficient  resistance  is  provided  to  carry  the 
full  load  current  continuously. 

Ques.    What  is  meant  by  self  induction? 

Ans.  A  characteristic  of  alternating  current  circuits, 
where  the  current  tends  to  create  a  counter  E.  M.  F. 
Self  induction  varies  greatly  with  conditions  depending 
upon  the  arrangement  of  the  circuit,  the  medium  sur- 
rounding the  circuit,  the  devices  or  apparatus  supplied 
or  connected  in  the  circuit,  etc.  For  example,  if  a  coil 
having  a  resistance  of  100  ohms  is  included  in  the  cir- 
cuit, a  current  of  one  ampere  can  be  passed  through 
the  coil  with  an  electric  pressure  of  100  volts,  if  direct 
current  is  used;  while  it  might  require  a  potential  of 


MOTION      PICTURE      PROJECTION  113 

several  hundred  volts  to  pass  a  current  of  one  ampere 
if  alternating  current  is  used,  depending  upon  the 
number  of  turns  in  the  coil,  whether  it  is  wound  on  iron 
or  some  other  non-magnetic  material. 

Ques.  State  six  reasons  for  the  film  jumping  on  the 
screen. 

Ans.  Dirt  on  sprockets,  especially  the  intermittent 
sprocket,  losing  the  bottom  loop,  not  enough  tension  in 
gate  of  machine,  sprocket  shaft  not  true,  shaft  bushings 
badly  worn,  holes  in  the  films  worn. 

Ques.    Suppose  you  blow  the  fuse  when  you  strike 
the  arc,  where  would  you  look  for  the  trouble? 
Ans.    In  the  rheostat. 

Ques.    Suppose  you  blow  the  fuse  when  you  close  the 
table  switch,  where  would  you  look  for  the  trouble? 
Ans.    Between  the  table  switch  and  the  arc  lamp. 

Ques.  If  you  strike  the  arc  and  only  get  a  spark  and 
carbons  refuse  to  hold  arc  where  would  you  look  for  the 
trouble? 

Ans.  Loose  connection  or  oxidized  connection  in 
rheostat  or  on  line. 

Ques.  Is  it  possible  to  get  a  fire  on  the  machine,  if 
so  how? 

Ans.  Yes,  bad  patches  in  film  opening  up  while 
going  through  machine,  torn  sprocket  holes  on  each 
side  of  film,  take-up  refusing  to  work,  automatic  shutter 
failing  to  work,  film  breaking  in  gate  between  upper  and 
intermittent  sprocket,  dirt  and  pieces  of  film  gathering 
in  film  aperture  in  gate. 


114  MOTION      PICTURE      PROJECTION 

Ques.  State  what  you  would  use  to  test  for  ground 
or  open  circuit  in  rheostat. 

Ans.    A  bell  set. 

Ques.  How  yould  you  test  for  ground  and  how  for 
open  circuit  in  rheostat? 

Ans.  First  test  bell  set  by  connecting  both  terminals 
together,  if  you  get  a  ring  then  set  is  all  right  and  proceed 
as  follows :  Place  one  of  the  terminals  of  bell  set  on  the 
frame  of  rheostat  and  the  other  terminal  on  the  first 
coil  or  plate  of  rheostat,  if  you  get  a  ring,  then  rheostat 
is  grounded.  If  you  do  not  get  a  ring  then  rheostat  is 
free  from  ground.  If  grounded,  to  locate  which  plate 
or  coil  is  causing  the  ground,  proceed  as  follows :  Place 
terminal  of  bell  set  on  frame  and  other  terminal  on 
first  coil,  if  you  get  a  ring,  disconnect  first  coil  then  test 
the  second  and  so  on  till  bell  stops  ringing.  As  soon  as 
bell  stops  ringing  it  signifies  that,  the  coil  that  you 
disconnected  last  is  the  coil  that  was  grounded. 

To  test  for  open  circuit,  place  the  terminals  of  bell 
set  on  the  terminals  on  rheostat  and  if  you  get  a  ring 
then  rheostat  is  O.K. 

Ques.  If  you  were  drawing  30  amperes  on  a  110  volt 
circuit,  how  many  kilowatts  would  you  be  using? 

Ans.  Volts  times  amperage  equals  watts,  so  110  x  30 
equals  3300,  and  as  there  are  1,000  watts  in  a  kilowatt 
that  means  that  we  have  3  3-10  K.  W. 

Ques.  How  would  you  measure  a  No.  6  rubber  cov- 
ered stranded  wire? 

Ans.  First,  scrape  off  the  insulation,  then  measure 
one  of  the  strands  with  a  B.  &  S.  wire  guage,  we  would 
find  that  this  strand  would  be  a  No.  14,  then  by  referring 


MOTION      PICTURE      PROJECTION  115 

to  the  wire  table  we  would  find  that  a  14  wire  contains 
4,107  circular  mils,  then  we  count  the  strands  in  the 
cable  and  we  find  there  are  seven,  so  we  multiply  4,107 
by  7  which  equals  28,749,  then  we  again  refer  to  wire 
table  to  find  the  nearest  number  to  28,749  which  is 
26,250  and  looking  across  wire  column  we  find  that  this 
is  a  No.  6  wire. 

Ques.  State  how  you  would  test  lamp  house  for 
grounds? 

Ans.  Take  test  lamp  and  after  making  sure  that 
there  was  current  in  the  lamp  house  (by  placing  test 
lamp  terminals  on  carbons)  would  proceed  as  follow: 
Would  place  one  terminal  of  test  lamp  on  the  upper 
carbon  and  the  other  terminal  on  lamp  house,  if  test 
lamp  lights,  then  the  lower  jaw  must  be  grounded,  if 
we  do  not  get  a  light  then  lower  jaw  is  O.K.  Then  we 
place  one  of  the  test  lamp  terminals  on  the  lower  jaw 
or  carbon  and  the  other  terminal  we  place  on  metal  of 
lamp  house,  if  we  get  a  light  then  the  upper  jaw  is 
grounded,  if  we  do  not  get  a  light  then  the  upper  jaw 
is  O.K.  If  machine  was  grounded  we  would  of  course 
remove  ground  wire  before  making  the  test  as  above. 

Ques.   Name  three  essential  parts  of  a  dynamo. 
Ans.    Armature,  commutator,  field  coils. 

Ques.   What  is  the  object  of  the  field  magnets? 

Ans.  To  provide  a  field  of  magnetic  lines  of  force 
to  be  cut  by  the  armature  inductors  as  they  revolve 
in  the  field. 

Ques.   What  is  an  armature? 


116  MOTION      PICTURE      PROJECTION 

Ans.  A  collection  of  inductors  mounted  on  a  shaft 
and  arranged  to  rotate  in  a  magnetic  field  with  provision 
for  collecting  the  current  induced  in  the  inductors. 

A  simple  loop  or  turn  of  wire  may  be  considered  as 
the  simplest  form  of  armature. 

Ques.   What  is  a  commutator? 

Ans.  A  device  for  causing  the  alternating  currents 
generated  in  the  armature  to  flow  in  the  same  direction 
in  the  external  circuit.  It  consists  of  a  series  of  copper 
bars  or  segments  arranged  side  by  side  forming  a  cylin- 
der and  insulated  from  each  other  by  sheets  of  mica. 

Ques.  How  do  armature  and  field  magnets  differ  in 
dynamos  and  alternators? 

Ans.  In  the  dynamo  the  field  magnet  is  the  station- 
ary part  and  the  armature  revolves.  While  in  an  alter- 
nator the  reverse  is  the  case. 

Ques.   Name  five  parts  of  a  dynamo. 

Ans.  Bed  plate,  field  magnets,  armature,  commu- 
tator, brushes. 

Ques.  The  primary  coil  of  a  transformer  is  supplied 
with  a  current  of  25  amperes  at  2,000  volts,  the  pressure 
received  from  the  secondary  is  250  volts.  What  is  the 
current  from  the  secondary  coil,  taking  it  for  granted 
that  the  transformer  is  100%  efficient? 

Ans.  Input  equals  output.  Input  is  2,000  times  25 
equals  50,000  watts.  Watts  divided  by  volts  equals 
amperes,  so  50,000  divided  by  250  equals  200.  Therefore 
the  current  from  the  secondary  is  200  amperes. 

Ques.  What  is  the  name  of  the  coil  in  which  the 
current  is  induced? 

Ans.    The  secondary. 


MOTION      PICTURE      PROJECTION  117 

Ques.  Does  a  transformer  take  any  current  when 
the  switch  on  the  lamp  side  of  same  is  open? 

Ans.    Yes.     A  no-load  passes  through  the  primary. 

Ques.    What  is  meant  by  an  oil  cooled  transformer? 

Ans.  A  transformer  filled  with  mineral  oil  to  help 
keep  the  transformer  cool,  never  used  on  moving  pic- 
ture work,  the  fire  risk  is  too  great. 

Ques.  What  would  cause  the  breaking  of  a  brand 
new  film  while  passing  through  the  machine,  taking  it 
for  granted  that  the  film  was  handed  to  you  in  perfect 
condition,  and  that  you  had  just  run  some  six  or  seven 
reels  of  film  through  the  machine  without  mishap? 

Ans.  Caused  by  the  emulsion  coming  off  the  new 
film  and  adhering  to  the  tension  bars  in  gate  of  machine, 
which  would  give  undue  tension  to  the  film. 

Ques.  What  is  meant  by  fading  a  picture?  When 
and  how  is  it  done? 

Ans.  Fading  is  done  by  the  gradual  cutting  off  of 
the  light  (either  when  taking  or  projecting  the  picture) . 
The  operator  fades  one  reel  into  the  other  when  chang- 
ing from  one  machine  to  the  other.  This  is  accom- 
plished by  the  dowsers  on  the  machines,  by  slowly 
closing  one  and  at  the  same  time  slowly  opening  the 
other. 

Ques.  On  which  coil  of  an  economizer  is  the  greatest 
wattage? 

Ans.  As  transformers  are  not  100%  efficient  there 
is  a  loss  in  transforming  the  current,  this  loss  amounts 
to  approximately  5%  and  as  the  output  equals  the  input 
less  the  loss,  it  will  mean  that  we  have  more  wattage 
on  the  primary  than  on  the  secondary. 


118  MOTION      PICTURE      PROJECTION 

Ques.  What  is  the  proper  rate  of  speed  of  showing 
a  1,000  feet  of  film? 

Ans.  About  fifteen  to  seventeen  minutes.  Or  about 
sixteen  pictures  to  the  second. 

Ques.  if  the  machine  is  running  at  proper  speed 
(sixteen  pictures  to  the  second)  about  how  long  is  each 
picture  held  on  the  screen? 

Ans.  For  one-sixteenth  part  of  a  second  less  the  time 
it  takes  the  intermittent  sprocket  to  move  the  film. 

Ques.  Mention  some  of  the  different  makes  of  moving 
picture  machines. 

Ans.  Powers,  Simplex,  Standard,  Motiograph,  Baird, 
Edison,  Lubin,  Pathe,  Kinemacolor,  Cameron. 

Ques.  Which  would  show  the  greater  saving,  a  D.  C. 
economizer  or  rheostats? 

Ans.  The  initial  cost  of  the  D.  C.  economizer  would 
•be  greater  than  that  of  rheostats,  but  the  working  cost 
of  the  D.  C.  economizer  would  show  a  great  saving  over 
that  of  the  rheostats. 

Ques.  Why  are  flicker  shutters  made  with  two  or 
three  blades  when  only  the  largest  blade  is  used  to  cut 
off  the  picture  from  screen  while  the  film  is  in  motion 
in  gate  of  machine? 

Ans.  The  second  and  third  blades  are  on  to  equalize 
the  light. 

Ques.    What  is  a  wire  gauge? 

Ans.    A  gauge  used  to  measure  wires. 

Ques.  What  is  the  difference  between  Greenfield  and 
B.  X.? 

Ans.  Greenfield  is  a  metal  tubing  without  wires 
while  B.  X.  is  the  same  tubing  with  wires. 


.MOTION      PICTURE      PROJECTION  119 

Ques.  What  is  the  difference  between  a  D.  C.  con- 
verter and  a  rotary  converter? 

Ans.  A  D.  C.  converter  converts  D.  C.  to  D.  C. 
while  the  rotary  converter  converts  A.  C.  to  D.  C. 

Ques.    What  is  meant  by  a  circuit? 

Ans.    The  path  in  which  the  current  flows. 

Ques.    What  is  a  closed  circuit? 

Ans.  When  all  switches,  etc.,  on  a  line  are  closed 
giving  the  current  a  continuous  path. 

Ques.    What  is  meant  by  insulation? 
Ans.    Some  non-conducting  material  on  or  around  a 
conductor  to  prevent  the  escape  of  current. 

Ques.  Show  by  sketch  how  a  lens  is  set  and  how  it 
works. 

Ans.    See  page  75. 

Ques.    What  is  a  circuit  breaker? 

Ans.  A  switch  which  opens  automatically  when  the 
current  or  pressure  exceeds  or  falls  below  a  certain  fixed 
standard. 

Ques.  What  effect  has  it  by  connecting  dynamos  in 
series  and  dynamos  in  multiple? 

Ans.  Dynamos  in  series  increase  the  volts,  dynamos 
in  multiple  increase  the  amperes. 

Ques.  Name  a  number  of  good  conductors,  fair  con- 
ductors and  non-conductors. 

Ans.  Silver,  copper,  mercury  and  aluminum  are 
good  conductors.  Water,  the  body,  and  dry  wood  are 
partial  conductors  and  mica,  slate,  glass  are  non- 
conductors. 


120  MOTION     PICTURE     PROJECTION 

Ques.    What  is  the  inverse  of  resistance? 
Ans.    Conductivity. 

Ques.  State  one  of  the  disadvantages  of  using  A.  C. 
for  motion  picture  work. 

Ans.  Both  carbons  form  a  crater  and  the  arc  keeps 
traveling  around  carbons  making  it  difficult  to  get  a 
good  steady  light  on  screen. 

Ques.    Of  what  use  is  the  field  magnet  in  a  dynamo? 
Ans.    To  provide  a  field  of  lines  of  force  to  be  cut  by 
the  armature  inductors. 

Ques.  State  one  of  the  advantages  of  A.  C.  over 
D.  C.  as  far  as  transmission  goes. 

Ans.  Reduces  the  cost  of  transmission  by  using  high 
voltage  and  transformers. 

Ques.    What  is  the  armature? 

Ans.  A  collection  of  inductors  mounted  on  a  shaft 
and  arranged  to  turn  in  a  magnetic  field  for  collecting 
the  current  induced  in  the  inductors. 

Ques.    What  is  a  commutator? 

Ans.  A  device  for  causing  the  alternating  currents 
generated  in  the  armature  to  flow  in  the  same  direction 
in  the  external  circuit. 

Ques.    Which  end  of  the  lens  faces  arc? 
Ans.    The  flat  or  lesser  convex  end. 

Ques.  What  would  you  use  to  scrape  off  the  emul- 
sion from  tension  bars? 

Ans.    Copper  or  any  soft  metal. 

Ques.    Where  is  the  most  luminous  part  of  an  arc? 
Ans.    In  the  crater  of  the  positive  carbon. 


MOTION      PICTURE      PROJECTION  121 

Ques.    What  causes  hissing  of  an  electric  arc? 

Ans.  Feeding  carbons  too  close  together,  feeding  it 
a  higher  current  than  that  required  for  the  length  of 
arc  employed. 

Ques.  What  is  the  reason  of  using  a  cored  carbon  in 
the  positive  jaw  of  arc? 

Ans.  To  reduce  the  voltage  required  to  maintain 
the  arc  by  lowering  the  boiling  point  or  the  vaporizing 
temperature  of  the  crater. 

Ques.    State  the  advantages  of  rubber  as  an  insulator. 
Ans.    It  is  flexible,  fairly  strong  and  waterproof. 

Ques.  Can  you  use  a  bell  set  to  find  ground  in  lamp 
house? 

Ans.  Yes.  Place  one  terminal  of  bell  set  on  upper 
carbon  and  other  terminal  on  lamp  house  frame,  if  bell 
rings  then  the  upper  jaw  is  grounded,  if  no  ring  then 
upper  jaw  is  O.K.  Then  place  one  terminal  of  bell  set 
on  lower  carbon  and  other  terminal  on  lamp  house  if 
bell  rings  then  the  lower  jaw  is  grounded,  if  you  do  not 
get  a  ring  then  lower  jaw  is  O.K. 

Ques.    How  often  would  you  test  lamp  house  for 
grounds? 
Ans.    Before  show  each  day. 

Ques.  Suppose  you  found  that  either  the  upper  or 
lower  jaw  was  grounded,  where  would  you  first  look  for 
the  trouble? 

Ans.  Probably  the  mica  insulation  has  worked  out 
of  jaws  of  lamp. 


122  MOTION     PICTURE     PROJECTION 

Ques.    Describe  fully  what  is  meant  by  an  electric  arc. 

Ans,  Suppose  two  carbons  are  connected  in  an  elec- 
tric circuit,  and  the  circuit  closed  by  touching  the  tips 
of  the  carbons  together  (striking  your  arc);  on  separ- 
ating these  carbons  again  the  circuit  will  not  be  broken, 
providing  the  space  between  be  not  too  great,  but  will 
be  maintained  through  the  arc  formed  at  this  point. 
The  current  is  assumed  as  passing  from  the  upper 
carbon  (positive)  to  the  lower  carbon  (negative).  We 
find  in  a  direct  current  arc  that  most  of  the  light  issues 
from  the  tip  of  the  positive  carbon,  and  this  portion  is 
called  the  crater  of  the  arc.  The  lower  carbon  becomes 
pointed  as  the  upper  one  hollows  out  to  form  the  crater. 
The  negative  carbon  is  also  incandescent,  but  not  to  the 
same  extent  as  the  positive.  Between  the  carbons  there 
is  a  band  of  violet  light  (the  arc  proper)  -and  this  is  sur- 
rounded by  a  luminous  zone  of  a  golden  yellow  color. 
The  carbons  are  worn  away  or  consumed  by  the  pas- 
sage of  the  current.  The  positive  carbon  being  con- 
sumed about  twice  as  quick  as  the  lower. 

With  alternating  current  the  upper  carbon  becomes 
positive  and  negative  alternately,  and  there  is  no  chance 
for  a  good  crater  to  be  formed,  both  carbons  giving  off 
the  same  amount  of  light  and  being  consumed  at  about 
the  same  rate. 

Ques.  What  is  a  voltmeter  used  for  and  how  would 
you  connect  same? 

Ans.  Use  to  measure  the  pressure  or  voltage,  con- 
nected in  multiple  on  your  line. 

Ques.    What  is  an  ammeter  and  how  is  it  connected? 

Ans.  Used  to  measure  the  current  or  amperage,  con- 
nected in  series  on  the  line. 


MOTIOX      PICTURE      PROJECTION  123 

Ques.  State  what  care  you  would  take  of  film  while 
it  is  in  your  charge. 

Ans.  Would  examine  all  film  before  showing,  keep 
each  reel  in  a  metal  box  or  can,  and  keep  all  these  cans 
in  another  metal  box  constructed  without  solder  and 
with  a  self-closing  door. 

Ques.    Name  three  causes  of  sparking  at  your  motor. 

Ans.  Dirt,  uneven  brushes  and  broken  segment  in 
the  commutator. 

Ques.  Under  what  conditions  can  you  rewind  film  in 
the  booth? 

Ans.  Never  rewind  films  in  booth  while  arc  is  burn- 
ing, or  while  audience  is  in  theatre. 

Ques.    What  would  you  do  in  case  of  fire  in  the  booth  ? 

Ans.  Stop  motor  and  switch  off  arc,  drop  the  booth 
shutters,  turn  on  the  house  lights,  notify  manager  and 
try  and  extinguish  fire. 

Ques.  What  precautions  would  you  take  to  prevent 
fires? 

Ans.  Keep  all  films  in  fireproof  cans,  only  have  the 
film  on  the  way  to  the  machine  exposed  at  any  time, 
keep  booth  free  from  all  pieces  of  film  and  all  combus- 
tible material,  see  that  take-up  and  automatic  shutter 
work  O.K.,  keep  lamp  house  free  from  all  grounds, 
keep  all  electrical  connections  tight,  keep  machine  clean 
and  in  good  running  order,  have  a  bucket  of  water  and 
one  of  sand  near  at  hand  in  booth,  place  all  hot  carbons 
into  a  bucket  of  water  when  you  take  them  from  arc 
lamp. 

Ques.  How  would  you  adjust  the  take-up  without 
stopping  the  machine? 


124  MOTION      PICTURE      PROJECTION 

Ans,  If  the  belt  was  slipping  would  use  a  little  rosin 
or  tighten  up  the  tension  screw,  or  use  the  idler  pulley 
if  machine  was  equipped  with  one.  If  take-up  refused 
to  revolve  the  bottom  reel,  would  stop  machine  and  fix. 

Ques.    Why  do  they  ground  an  all  metal  machine? 
Ans.    For  safety, 

Ques.  How  would  you  find  the  amount  of  resistance 
offered  by  any  conductor? 

Ans.  The  resistance  of  any  conductor  is  equal  to  its 
length  in  feet  divided  by  the  area  in  circular  mils  mul- 
tiplied by  the  resistance  per  mil-foot  (which  is  10.5 
ohms) . 

Ques.    What  is  the  international  ohm? 

Ans.  The  resistance  offered  by  a  column  of  pure 
mercury  106.3  centimeters  in  length  by  one  square  milli- 
meter in  cross  section  at  a  temperature  of  zero  centi- 
grade. 

Ques.  What  percentage  of  light  is  lost  between  the 
arc  lamp  and  the  screen? 

Ans.  Take  the  crater  of  arc  as  100%,  only  33%  of 
this  is  picked  up  by  the  condensers  on  D.  C.  (On 
A.  C.  the  percentage  is  much  less).  Then  there  is  a 
16%  reflection  loss  (4%  at  each  of  the  four  glass- to-air 
surfaces  of  condensers)  plus  an  absorption  loss  of  9% 
(absorption  loss  being  reckoned  as  6%  per  inch,  and 
assuming  the  condenser  combination  to  have  an  axial 
thickness  of  1^2  inch)  or  in  other  words  the  light  fall- 
ing upon  the  condensers  is  subjected  to  a  reduction  of 
25%  in  passing  through  them.  Thus  only  25.75% 
passes  on  to  the  film  being  projected.  About  50%  of 


MOTION     PICTURE     PROJECTION  125 

this  light  will  be  lost  passing  through  the  film,  so  that 
only  12.85%  is  sent  on  to  projection  lens.  In  its  pas- 
sage through  the  objective  lens  the  light  is  further  re- 
duced some  25%  in  intensity  (4%  reflection  loss  at  each 
of  the  six  glass-to-air  surfaces)  therefore  but  9.65% 
emerges  from  lens.  This  is  again  cut  50%  by  the 
flicker  shutter,  leaving  only  4.80%  of  the  original 
amount  emanating  from  arc  lamp  for  the  illumination 
of  the  screen  picture.  Other  factors  such  as  the  dis- 
tance to  screen  and  the  effective  aperture  of  the  ob- 
jective also  enter,  so  this  is  only  a  rough  approximation. 

Ques.   What  is  a  six  to  one  intermittent  movement? 

Ans.  A  movement  with  which  each  picture  on  the 
film  is  moved  into  place  before  the  aperture  of  the 
projector  in  an  interval  of  time  equal  to  one-sixth  of 
the  period  required  for  a  complete  revolution  of  its 
driving  member  (cam). 

Ques.  Is  both  voltage  and  amperage  used  up  in  arc 
lamp,  or  is  the  voltage  used  up  and  amperage  returned; 
or  is  the  voltage  returned  to  dynamo  and  amperage 
used  up  at  arc? 

Ans.  The  voltage  is  used  up  forcing  the  amperage 
through  the  resistance.  The  amperage  returns  to 
dynamo.  This  can  be  proved  by  connecting  an  am- 
meter in  your  circuit. 

Ques.  What  would  be  the  result  if  you  lost  your 
bottom  loop? 

Ans.    Film  would  jump  or  break. 

Ques.  What  regulates  the  speed  of  the  reels  in  the 
upper  and  lower  magazines. 


126 


MOTION      PICTURE      PROJECTION 


Ans.  The  top  reel  is  regulated  by  film  tension  and 
the  lower  is  regulated  by  the  tension  spring  and  split 
pulley. 

Ques.  Of  what  use  is  the  flicker  shutter  on  head  of 
machine? 

Ans.  To  cut  off  the  rays  of  light  from  screen  while 
the  film  is  in  motion  in  gate. 

Ques.    What  causes  the  film  to  remain  stationary  in 
gate  of  machine? 
Ans.    The  intermittent  movement. 

Ques.    What  is  it  that  works  the  automatic  shutter? 
Ans.    The  centrifugal  movement. 


B.  and  S.  Gauge 


MOTION      PICTURE      PROJECTION  127 


Head  of  Powers' No.  6 


128 


MOTION      PICTURE      PROJECTION 


MOTION      PICTURE      PROJECTION  129 


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NEW  YORK  CITY 

The  Operator's  License  and  copy  of  these  rules  shall 
be  displayed  in  a  conspicuous  place  in  the  booth  while 
the  public  is  in  or  has  access  to  the  premises. 

No  operator  shall  conduct  an  exhibition  except  where 
to  his  knowledge  a  permit  or  license  of  the  department 
of  licenses  is  exhibited  on  the  premises. 

The  apparatus  and  its  construction  shall  be  tested 
by  the  operator  prior  to  each  performance.  No  defec- 
tive apparatus,  or  apparatus  of  a  type  not  approved 
by  this  department  shall  be  operated.  No  apparatus 
with  a  lamp  served  with  oxy-hydrogen  or  acetylene 
gas  shall  be  approved. 

It  is  forbidden  to  overfuse  (see  electrical  code, 
section  418  of  the  Code  of  Ordinances)  or  to  make  any 
electrical  connections  not  sanctioned  by  the  aforesaid 
chapter  (see  section  438). 

The  operator  shall  report  promptly  every  defect  in 
the  apparatus  or  its  connection,  the  correction  of  which 
he  is  unable  to  secure. 

Badly  torn  films  shall  not  be  used  and  their  presence 
in  the  booth  shall  be  reported  as  soon  as  practical. 

The  booth  at  all  times  shall  be  kept  clean.  No  pieces 
of  film  or  loose  combustible  material  shall  be  allowed 
to  remain  in  the  booth,  unless  kept  in  a  metal  box  pro- 


130  MOTION      PICTURE      PROJECTION 

vided  with  a  close  fitting  cover  constructed  without 
the  use  of  solder. 

The  door  of  the  booth  shall  be  kept  closed  while  the 
public  has  access  to  the  premises. 

No  person  shall  be  allowed  in  the  booth  except  the 
manager  or  owner  of  the  premises,  a  licensed  operator, 
a  person  specially  authorized  by  the  commissioner  in 
writing,  or  any  duly  accredited  officer  of  the  city. 

The  interior  of  the  booth  shall  remain  readily  acces- 
sible to  the  persons  mentioned  in  the  foregoing  section. 
The  door  of  the  booth  shall  not  be  latched  on  the  inside 
nor  the  handle  removed  from  the  outside,  nor  shall  any 
signalling  device  be  permitted  which  is  operated  from 
the  front  of  the  house. 

No  film  other  than  that  on  the  machine  or  on  the 
rewinder  shall  be  exposed  in  the  booth  at  any  time. 

No  smoking  is  permitted  in  the  booth  at  any  time. 

No  matches,  fire  or  open  light  is  permitted  in  the 
booth  while  the  public  is  on  or  has  access  to  the  house 
or  premises. 

Every  fire,  together  with  the  apparent  cause  thereof, 
shall  be  promptly  reported. 

Advance  report  shall  be  made  of  the  installation  of  a 
moving  picture  machine  for  a  one  night  exhibition. 

The  apparatus  shall  at  all  times  be  in  charge  of  a 
licensed  operator. 

It  is  forbidden  to  operate  while  under  the  influence 
of  liquor  or  drug  or  to  read  while  operating. 

Certificates  shall  not  be  loaned  or  transferred. 


MOTION      PICTURE      PROJECTION  131 


POINTS  TO  REMEMBER 

To  find  the  positive  or  negative  polarity  when  con- 
nected up,  strike  the  arc  and  let  same  burn  for  a  second 
or  two,  then  throw  off  the  switch  and  look  to  see  which 
of  the  carbons  cool  off  first.  Whichever  remains  red  the 
longest  is  the  positive  and  this  should  always  be  the 
carbon  in  the  top  jaw  of  lamp. 

If  you  find  that  the  lower  carbon  remains  red  longer 
than  the  top,  then  your  lamp  is  burning  upside  down, 
or  in  other  words  the  positive  line  is  connected  to  the 
lower  jaw  instead  of  the  top.  This  can  be  remedied 
by  changing  the  wires  at  arc,  wall,  wall-switch,  or  table- 
switch. 

Should  both  carbons  remain  red  the  same  length  of 
time  you  have  alternating  current. 

The  Department  of  Water  Supply,  Gas  and  Electric- 
ity call  for  the  use  of  link  fuses  in  the  operating  booth  on 
the  machine  line.  Cartridge  fuses  are  not  allowed. 

Always  see  that  all  connections  are  tight  and  that 
lamp  house,  etc.,  is  free  from  grounds. 

Examine  the  lamp  leads  every  so  often,  remember 
that  copper  oxidizes  when  overheated. 

See  that  you  have  enough  carbon  in  holders  to  run 
the  reel  through. 

When  buying  or  fitting  condensers  and  mounts  for 
same,  remember  to  leave  room  in  mounts  for  the 
expansion  and  contraction  of  condensers.  Remember 
that  cold  draughts  will  break  your  condensers. 


132  MOTION      PICTURE      PROJECTION 

To  Set  the  Flicker  Shutter.  To  set  the  flicker  shutter, 
loosen  up  the  set  screw  so  that  shutter  revolves  freely 
on  the  shaft,  now  turn  shutter  till  single  set  screw  is  in 
groove  of  shaft  and  then  tighten,  now  loosen  the  two 
screws  on  the  collar  and  open  the  gate  of  machine. 
Turn  the  balance  wheel  till  you  see  that  the  intermittent 
movement  is  just  about  to  revolve,  then  the  large 
blade  of  shutter  should  just  be  coming  up  to  cover  lens, 
and  should  be  so  fixed  that  the  blade  of  shutter  is  cover- 
ing the  front  of  lens  as  long  as  the  intermittent  sprocket 
is  in  motion. 

Another  way  to  set  it  is  as  follows :  Turn  the  balance 
wheel  till  two  teeth  of  the  intermittent  sprocket  has 
passed  a  given  point,  this  represents  one-half  of  a  picture 
or  in  other  words  that  the  picture  has  completed  one- 
half  of  its  movement,  now  set  the  large  blade  of  the 
flicker  shutter  dead  over  the  front  of  lens. 

Always  set  the  flicker  shutter  as  close  to  the  lens  as 
possible  leaving  enough  room  to  focus  the  lens. 

Always  keep  carbon  holders  clean  so  that  carbons 
make  good  contact. 

Always  have  a  spare  belt  (driving  and  take-up)  near 
at  hand. 

Keep  your  fingers  off  the  glass  surfaces  of  lenses. 

Oil  machine  often  a  little  at  a  time,  keep  oil  off  the 
floor  of  the  booth. 

Keep  oil  off  the  friction  discs. 

Never  use  oil  on  the  arc  lamp.    Use  graphite. 

Renew  motor  brushes,  whenever  necessary,  and  keep 
grease  cups  filled. 

Use  your  head  more  and  the  "One  minute  please" 
slide  less. 


MOTION     PICTURE     PROJECTION  133 


EXAMINATION  QUESTIONS 

1.  Name  some  of  the  different  lenses  used  in  moving 
picture  work. 

2.  Under  what  conditions  can  you  rewind  films  in  the 
booth? 

3.  To  which  end  of  the  table  switch  (lamp  or  line) 
would  you  connect  the  primary  coil  of  a  transformer? 

4.  How  is  a  transformer  constructed  and  how  does  it 
work? 

5.  How  would  you  judge  what  size  fuse  to  use  on 
a  line? 

6.  How  is  a  rheostat  made,  and  what  is  it  used  for? 

7.  Name  three  kinds  of  wires  used  in  moving  picture 
work. 

8.  What  is  meant  by  induction? 

9.  State  the  difference  between  an  auto  transformer 
and  a  step -down  transformer. 

10.  How  would  you  ground  an  all  metal  machine, 
and  after  you  have  same  grounded  would  you  expect 
to  get  a  light  with  test  lamp  if  you  connected  it  between 
either  carbon  of  arc  lamp  and  the  lamp  house  frame? 

11.  Name  three  causes  of  sparking  at  your  motor. 

12.  What  would  happen  if  the  neutral  fuse  on  a  three 
wire  system  was  to  melt,  providing  the  system  was 
balanced? 

13.  Explain  fully  what  is  meant  by  a  D.  C.  econo- 
mizer. 

14.  Show  by  sketch  the  setting  of  a  D.  C.  arc  and  a 
jack-knife  setting. 


134  MOTION     PICTURE     PROJECTION 

15.  Which  fuse  would  you  remove  first  on  a  three 
wire  system  and  give  reason  why? 

16.  Where  is  a  transverter  used  on  A.  C.  or  D.  C.? 

17.  What  is  meant  by  stealing  the  arc? 

18.  Is  the  primary  coil  of  an  economizer  connected 
in  series  or  multiple  on  your  line? 

19.  Is  there  any  difference  in  the  construction  of  a 
step-up  and  a  step-down  transformer,  which  is  used  for 
moving  picture  work? 

20.  Describe  fully  what  regulates  the  speed  of  a 
Powers,  Simplex  and  a  Standard  machine. 

21.  Do  you  get  A.  C.  or  D.  C.  from  the  secondary 
coil  of  a  transformer? 

22.  Does  the  resistance  of  metals  and  carbons  in- 
crease or  decrease  with  an  increase  of  temperature? 

23.  What  is  a  rectifier  used  for? 

24.  Name  the  fire  prevention  devices  on  the  head  of 
machine. 

25.  What  controls  the  size  of  the  picture  on  the 
screen? 

26.  What  precautions  would  you  take  before  starting 
your  show? 

27.  How  many  sets  of  fuses  would  you  use  on  your 
line  and  what  would  you  call  them? 

28.  Of  what  use  are  the  condensers? 

29.  Suppose  when  you  struck  the  arc  the  fuse  melted 
where  would  you  look  for  the  trouble? 

30.  How  are  the  coils  in  a  transformer  connected,  in 
multiple  or  series? 

31.  What  would  you  do  in  case  of  fire? 

32.  Show  by  sketch  how  a  lens  works  and  how  it  is 
put  together? 


MOTION      PICTURE      PROJECTION  135 

33.  What  is  the  carrying  capacity  of  a  No.  6,  a  No. 
8,  a  No.  14  rubbeer  covered  wire? 

34.  Name  the  mechanical  and  electrical  safety  de- 
vices on  the  machine  and  on  the  line. 

35.  What  precautions  must  you  take  when  on  a 
three  wire  system? 

36.  Give  an  easy  way  to  test  for  A.  C.  or  D.  C. 

37.  What  is  the  back  focal  length  of  a  lens? 

38.  Name  the  advantages  and  disadvantages  of  a 
three  wire  system.    State  how  a  three  wire  system  is 
obtained. 

39.  What  would  you  use  to  change  D.  C.  to  A.  C.? 
Is  this  ever  done  for  moving  picture  work?    If  so,  state 
when? 

40.  What  is  a  keystone  effect  on  screen? 

41.  What  is  ohms  law? 

42.  What  is  a  converter  and  where  is  it  used? 

43.  What  is  the  difference  in  construction  between  a 
step-down   transformer,    an   economizer,    and   an  in- 
ductor? 

44.  What  is  meant  by  current  frequency.     Do  we 
get  current  frequency  on  D.  C.? 

45.  What  is  a  kilowatt,  and  a  circular  mil? 

46.  Show  by  sketch  two  rheostats  connected  in  mul- 
tiple with  each  other  and  in  series  on  your  line.    State 
where  you  would  use  them. 

47.  With  two  110  volt  25  ampere  rheostats  connected 
in  series,  how  much  resistance  (in  ohms)  will  they  offer 
in  our  circuit? 

48.  What  is  an  electric  arc? 

49.  Explain  how  you  would  test  lamp  house  and 
rheostat  for  ground. 


136 MOTION     PICTURE      PROJECTION 

50.  What  size  wire  would  you  use  for  motor  connec- 
tions and  what  size  fuse? 

51.  Show  by  sketch  two  machines  connected  to  one 
source  of  supply. 

52.  On  which  line,  positive  or  negative,  would  you 
connect  your  rheostat? 

53.  What  is  the  difference  between  A.  C.  and  D.  C.? 

54.  State  what  combination  of  carbons  you  would 
use  if  you  were  drawing  50  amperes  D.  C. 

55.  Name  the  principal  parts  of  a  dynamo. 

56.  How  do  you  get  the  equivalent  focus  of  a  lens? 

57.  Explain   what   the   flicker   or  light   shutter  is 
used  for. 

58.  What  is  a  lug? 

59.  Name  six  causes  of  the  film  jumping  on  screen. 

60.  What  is  the  difference  between  a  short  circuit 
and  a  ground? 

61.  State  if  there  would  be  any  saving,  if  you  in- 
stalled an  economizer  in  place  of  a  rheostat  on  110  volt 
A.  C.  circuit. 

62.  State  how  you  would  go  about  measuring  a 
stranded  and  a  solid  wire. 

63.  With  two  1 10  volt  25  ampere  rheostats  connected 
in  multiple,  how  much  resistance  in  ohms  would  they 
offer  on  our  line? 

64.  Show  by  sketch  a  complete  circuit  from  the  main 
fuses  in  cellar  up  to  arc  lamp,  taking  it  for  granted  that 
you  have  220  volts  D.  C.  to  work  on. 

65.  Show  by  sketch  a  complete  circuit  using  a  trans- 
former. 

66.  Suppose  the  output  of  a  transformer  was  2,500 
watts,  50  volts,  what  would  be  the  amount  of  amperage? 


MOTION     PICTURE     PROJECTION  137 

67.  If  you    connected   three    110  volt  50   ampere 
rheostats  in  series,and  connected  them  on  a  220  source 
of  supply  what  approximate  amperage  would  this  give 
you  at  arc  lamp? 

68.  What  would  be  the  ohmic  resistance  of  three 
110  volts  30  ampere  rheostats,  connected  in  series? 

69.  What  is  the  voltage,  if  we  have  4  1-2  ohms  re- 
sistance on  line  and  are  getting  35  amperes  at  arc  lamp. 

70.  Connected  between  the  neutral  and  positive  wire 
of  a  three  wire  system  and  with  4  2-5  ohms  resistance 
on  circuit,  what  amperage  have  we  at  arc  lamp? 

71.  When  and  how  is  fading  done? 

72.  On  which  coil  of  a  transformer,  the  primary  or 
secondary,  is  the  most  wattage  and  give  your  reason 
for  this. 

73.;  State  fully  what  precautions  you  would  take  so 
that  you  could  project  a  picture  free  from  frame-ups. 

74.  By  what  would  you  judge  the  proper  rate  of 
speed  in  projecting  pictures,  how  long  should  it  take  you 
to  run  off  a  2000  foot  reel? 

75.  What  is  the  wattage  on  a  mazda  lamp  used  for 
moving  picture  projection  work? 

76.  How  would  you  measure  a  stranded  wire? 

77.  Name  six  parts  on  a  motor  generator  and  state 
their  uses. 

78.  What  size  fuse  would  you  install  providing  you 
were  connected  up  on  a  220  volt  circuit  and  had  two 
110  volt  25  ampere  rheostats  on  your  line? 

79.  Name  three  causes  of  your  film  breaking. 

80.  What  lubricant  would  you  use  on  the  following 
parts  of  the  machine?    (a)  Arc  lamp?    (6)  Intermittent 
movement? ,  (c)  Gears?    (d)  Motor  bearings? 


138  MOTION     PICTURE     PROJECTION 

81.  Which  would  be  the  cheaper  to  install  and  which 
the  cheapest  as  far  as  operating  cost,  a  D.  C.  economizer 
or  rheostats? 

82.  What  would  cause  the  breaking  of  a  brand  new 
film  while  passing  through  machine?    Is  there  any  way 
to  help  overcome  this? 

83.  What  is  meant  by  a  travel  ghost,  how  would  you 
remedy  same? 

84.  State  the  working  principal  of  a  Powers  inter- 
mittent movement. 

85.  Why  are  flicker  shutters  made  with  more  than 
one 'blade? 

86.  Of  what  use  is  the  loop  setter  and  on  which  make 
of  machine  will  you  find  same? 

87.  Is  it  possible  to  take  out  a  travel  ghost  while  the 
machine  is  in  motion,  if  so  how  would  you  go  about  it? 

88.  What  is  a  pin  cross  and  where  on  the  machine 
is  it  situated? 

89.  How  should  fuses  be  installed? 

90.  State  one  of  the  disadvantages  of  A.  C.  current 
for  moving  picture  work. 

91.  Is  it  possible  to  use  cored  carbons  on  D.  C.? 

92.  Name  three  good  conductors,  three  fan*  conduc- 
tors and  three  non-conductors* 

93.  What  is  meant  by  conductivity? 

94.  State  how  you  would  repair  a  torn  film. 

95.  How  would  you  determine  the  amount  of  am- 
perage that  would  flow  over  a  circuit  in  a  given  time? 

96.  What  effect  would  it  have  on  your  rheostat,  if 
you  changed  from  D.  C.  to  A.  C.? 

97.  How  would  you  find  the  saving  of  a  D.  C. 
economizer  or  a  motor-generator  set,  over  that  of  a 
rheostat? 


MOTION     PICTURE     PROJECTION  139 

98.  Are  there  any  precautions  that  should  be  taken 
with  new  film  to  prevent  the  breaking  of  same  while 
passing  through  the  machine? 

99.  Suppose  you  start  the  machine  and  you  find 
lower  reel  is  not  taking  up,  where  would  you  look  for 
the  trouble? 

100.  What  is  meant  by  the  armature?     Does  the 
armature  revolve  in  a  dynamo  and  alternator? 

101.  What  are  the  brushes  in  a  motor  made  of? 

102.  How  are  the  coils  or  plates  of  a  rheostat  con- 
nected, in  series  or  multiple? 

103.  What  is  meant  by  series  connection  and  multiple 
connection? 

104.  Suppose  the  film  broke  while  passing  through 
the  machine,  state  exactly  what  you  would  do. 

105.  Is   an   ammeter  and  voltmeter  connected   in 
series  or  multiple  on  your  line? 

106.  What  is  meant  by  reflection  and  refraction? 

107.  Why  do  we  get  double  the  voltage  and  not 
double  the  amperage,  when  connected  between  the  two 
outside  wires  of  a  three  wire  system? 

108.  What  is  meant  by  chromatic  aberration? 

109.  What  is  a  friction  disc  speed  regulator? 

110.  What  is  an  ampere-hour. 

111.  State  the  uses  of  following  parts  of  the  machine: 

(a)  Flicker  shutter  (g)  Fire  traps 

(6)  Balance  wheel  (h)  Framing  device 

(c)  Speed  regulator  (i)  Objective  lens 

(d)  Intermittent  movement  (j)  Condensers 

(e)  Tension  bars  (k)  Dowser 
(/)  Centrifugal  movement  (I)  Take-up 


140  MOTION     PICTURE      PROJECTION 

112.  State  how  you  would  clean  the  lenses  of  the 
machine,  and  what  you  would  use  for  this  purpose. 

113.  Why  not  use  a  cartridge  fuse  in  the  booth 
cut  out? 

114.  What  would  be  the  result  supposing  you  con- 
nected two  110  volt  25  ampere  rheostats  in  multiple,  on 
a  220  volt  circuit? 

115.  What  is  meant  by  a  balanced  circuit? 

116.  How  many  volts  will  a  No.  6  wire  carry? 

117.  What  is  stage  cable,  rubber  covered  wire,  and 
asbestos  wire? 

118.  State  in  your  own  way  how  we  are  deceived  into 
the  belief  of  motion  while  watching  pictures  oil  the  screen. 

119.  What  is  an  achromatic  lens? 

120.  What  is  a  ground?    What  is  a  short  "circuit? 

121.  State  how  it  is  possible  to  get  a  fire  on  head 
of  machine. 

122.  Does  a  transformer  change  A.  C.  to  D.  C.? 

123.  How  would  you  go  about  cleaning  the  head  of 
machine?    What  would  you  use  for  this  purpose? 

124.  What  is  meant  by  the  arc  lamp  burning  upside 
down?    How  would  you  remedy  this? 

125.  What  is  a  frame-up? 

126.  State  how  an  objective  lens  is  put  together  and 
say  exactly  what  it  does. 

127.  WTiat  is  the  principle  of  the  revolving  shutter 
and  how  would  you  time  it? 

128.  What  would  happen  if  a  coil  in  your  rheostat 
melted  out? 

129.  Show  by  sketch  two  machines  connected  to 
a  three  wire  system,  using  rheostats,  and  mark  the 
polarity  of  the  wires. 


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